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Preparation of benzothiophen compounds from bicyclic sulphides
PREPARATION OF BENZOTHIOPWEN COMPOUNDS FROM BICYCLIC SULPHIDES* A. N. K O R E P A N O V , T. A. DANILOVA and YE. A. VIKTOROVA M. V. Lomonosov State University,Moscow (Received 22 December 1975)
A STUDYwas made in this paper of dehydrogenation of 2- and 3-methyl-2,3-dihydrobenzothiophens and aehydro-isomerization of 2,2:dimethyl-2,3-dihydrobenzothiophen and thiochroman to corresponding benzothiophen compounds in the presence of catalyst with aprotonic acidity. TABLE 1.
FORMATION
OF
BENZOTHIOPHEN
COMPOUNDS
FROM
2-
A~D
3-METHY~L:2,3-DI-
HYDROBENZOTHIOPHENS
Space velocity 0.1 hr-~ Yield_____1%theo____~ Catalyst
•!P-
°c
~---7
I~'---'~
Overall
](x~F_~_CH,
N ~ / Y \ S / IN ~ / / \ { \ C I - I '
:Jbenzoth yield °f - Selec tivity,
N~//\S/[%i°phens'the°rY ]
%
2-Methyl -2, 3 -dihydrobenzothiophen 20% ZnCls/AliO 3 S a m e + 1% ionol Quartz AliO3 10% ZnC12/A1,O *
300
---
350
--
:
12
15 Traces
--
2 3
4
22 3 2o% zncl,/~,o,* 4 37 29 Quartz 400 3 6 AliO8 4 12 1 20% ZnCli/AliO s 11 15 14 3-Methyl:2,3-dihydrobenzothiophen 300 AlsOa 3 20% ZnCll/AlsO , -Traces 3 10% ZnC12/AI,O, 350 -3 9 20% ZnC1JAla0 , -14 19 i AlIOs 400 7 20% ZnC12/A120 s 13 20 20* * Found: 2% 2,3-dimethylbenzothiophen. ? Found: 3% 2.3-dtmethy]benzothiophen. --
18 0 4 25 72 9 17 44
85 84 0 80 85 89 100 61 76
3 3 12 33 7 56
100 50 65 67 61 96
Catalytic dehydrogenation of 2,3-dihydrobenzothiophen was previously carried out in the presence of chromium and copper applied on charcoal [1] and an alumina-chromium-beryllium catalyst [2]. It was shown subsequently * l~eftekhimiya 16, No. 6, 909-916, 1976. 242
Preparation of benzothiophen compounds from bicyclic sulphides
243
t h a t dehydrogenation of 2,3-dihydrobenzothiophen also takes place in the presence of alumlnosilicate having considerable aprotonic acidity [3] and on contact with 20% ZnC12]A1208, dehydro-isomerization of bicyclic sulphide (thiochroman) takes place with compression of the six-membered hetero-cycle, resulting, in a mixture of benzothiophen compounds [4, 5]. We used Al~O3, 10 and 20% ZnCl~/AI203 and an industrial spherical aluminosilicatc catalyst. The conversion of bicyelic sulphides was carried out in the temperature range of 300:-450 ° and at space velocities of 0.1-1.4 hr -1.
~Z % 88'
5
qO ,
12
F 2
4 ,i
1
C
%1
G
ZO,
#
0
300
i
350
f,°C q00
FIG. 1. Relation between the yield of benzothiophen compounds and temperature. 20~o ZnCls/A12Os; space velocity 0-1 hr-1; a--from 2-methyl-2,3-dihydrobenzothiophen; b--from 3-methyl-2,3-dihyctrobenzothiophen; c--from 2,2-dimethyl-2,3-d/hydrobenzothiophen. In Figs. 1-3: 1--benzothiophen; 2--2-methylbenzothiophen; 3--3-methylbenzothiophen; 4--2,3-dimethylbenzothiophen; 5--overall yield of benzothiophens; 6--process selectivity.
A. N. KOREPANOVet UL
244
Dehydrogenation of 2- and 3-methyl-2,3dihydrobenzothiophens took place on all catalyst samples under all kinds of reaction conditions. 2- and 3methylbenzothiophens and benzothiophens are the main products of the conversion of these sulphides. Benzothiophen was formed as a result of disproportionation of methylbenzothiophens [S]. In addition to benzothiophen, the catalysates contained methyl-2,3-dihydrobenzothiophen (isomer in relation to the initial products) and alkylbenzenes. It tollows from Table 1 and Fig. la and b that most satisfactory results were obtained in the presence of 20% ZnCl,/Al,O, at optimum temperatures of 350 and 375” using 2- and 3-methyl-2,3dihydrobenzothiophens, respectively for dehydrogenation on this catalyst. A shift in the maximum yield of benzothiophen compounds from 2-methyl-2,3dihydrobenzothiophen to low temperatures confirms an increased readiness to dehydrogenation. A reduction in the overall yields of benzothiophen compounds with an’ increase of temperature above the optimum value is due to an increase in the proportion of secondary processes (elimination of sulphur to form alkylbenzenes, deposition of products of condensation on the catalyst). Benzothiophen is an exception, the formation of which increases in a linear manner with an increase of temperature as a result of demethylation of homologues. Dehydrogenation takes place with a high degree of selectivity, which reaches 89 and 92% at optimum temperature for 2- and 3methyl-2,3-dihydrobenzothiophens, respectively (Fig. la and a). An increase in space velocity for sulphide reduces the yield of benzothiophens, process selectivity remaining practically unchanged. On contact with 10 and 20% ZnCl,/Al,OS at 300-400” and a space velocity of 0.1-03 hr-l 2,2-dimethyl-2,3-dihydrobenzothiophen is dehydro-isomerized mainly into 2,3dimethylbenzothiophen; the latter is partially demethylated into 2- and 3-methylbenzothiophens and benzothiophen (Table 2). In addition to benzothiophens, L-methylpropenyl phenyl sulphide (l-18%), 2,3dimethyl2,3-dihydrobenzothiophen* (1.6%) alkylbenzens (1-50/O) and thiophenol (l-3%) are formed. It follows from Table 2 that there is a direct relation between catalyst acidity and the overall yield of benzothiophen compounds. The effect of temperature on benzothiophen yield is shown in Fig. lc. The maximum yield of benzothiophens is 47-51%, independent of the variation of space velocity (O*l-0.8
hr-1).
The effect of space velocity on the overall yield of benzothiophens depends on experimental temperature: at 300 and 356’ its increase reduces yield; at 400” yield is practically independent of space velocity (Table 2), which is due to the low proportion of secondary processes. The maximum selectivity of the formation of benzothiophens reaches * IS O&
formed
at
300-350~.
Preparation of benzothiophen compounds from bieyelie sulphides
245
75% at 350 ° and at a low space velocity (0.1 hr-i) is practically independent of any further increase in temperature (Fig. lc). The main direction of conversion of thiochroman, on contact with 10 and 20% ZnCls/A1,O s or aluminosilieate, is dehydroisomerization, which products 2- and 3-methylbenzothiophens, benzothiophen and 2,3-dimethylbenzothioTABLE 2. F O R M A T I O N OF B E N Z O T H I O P H E N COMPOUNDS FROM 2 , 2 - D I M E T H Y L - 2 , 3 - D I H Y D R O BENZOTHIOPHEN
Yield, % theory
5
~
Catalyst
5 ~7
s
S
CHI
~; ~.~ I
kICI/A1203 to% ZnCld /AlIO3
300 350
Traces
0°1
--
300 350
0"1
300 300 300 350 350 350 400 400 400
0.1 0.4 0.8
Traces
Traces
Traces
3
3~
Traces
3 16
4 5( 18 5~
20% ZnCls/ /AlsO3
0.1
1
0.4 0.8 0.1 0.4 0.8
Traces 2 5 4 2
1 1 1 5 3
2 11 11 10
1
Traces 3 2 1
11 II 8
14 7 5 42 26 23 17 15 27
16 8 6 51 31 26 44 41 I 47
5( 4: 31 71 5: 5~ 7( 6~ 7:
phen. In the presence of A1203 isomerization of thiochroman to 2- and partly to 3-methyl-2,3-dihydrobenzothiophens is the prevailing process. The curve showing the dependence of the overall yield of b e n z o t h i o l ~ l ~ ~from thiochroman on catalyst acidity passes through the maximum wigh ~rerage acidity (Fig. 2). The ~emperature dependence of the overall yield of benzothiophens on the other hand follows a linear pattern (Fig. 3). Therefore, the maximum yield of benzothiophens from thiochroman was observed at 450 ° on contact with 10°/0 ZnC12/A120 a and was 52% with a selectivity of the process of 82% (Table 3, Fig. 2). During transformations of thiochroman in addition to benzothiophens, the following were formed under all conditions: alkylbenzenes (1-16%), thiophenol (1-6°/0),aad-2,.~ud 3-methyl-2,3-dihydrobenzothiophens. The amBunt
A. N. K o ~ . P ~ O V et al.
246
of the latter on contact with ZnCI~/AI~Oa, was negligible ( ~ 1%); in the presence of Al~03 on the other hand, it was 79%, the first isomer being predominant (74%); Selectivity of formation was 92%. An increase in space velocity reduced the yield of benzothiophens as a result of a lower degree of conversion of the initial sulphide (Table 3). It is significant that the qualitative composition of eatalysates obtained of three different sulphides (2- and 3-methyl-2,3-dihydrobenzothiophen and % 8O
8
~: qo 2o
!
0
0.5
l.O
1.5
Acidit~ , m-eTuiv.//9 FIe. 2. Relation between the yield of benzothiophen compounds prepared using thiochroman and the acidity of the catalyst. 450°; space velocity 0.1 hr -1. thioehroman) is the same. This suggests that conversions take place by a single mechanism. Conditions such as reaction only on contact with catalysts having aprotonic acidity (in the presence, for example, of A1203 modified with hydrochloric acid hardly any conversion takes place see Table 2) are as follows: presence on the catalyst surface of eentres capable of rupturing t h e % 80 I--
...I~°
.S ,,0~k1--°-" ..o-" ~...~ ..~0'~"
5
t
2° 1
JO0
5 -
350
6
o
zlO0
o
-2 a
Z¢50 t, °C
FIe. 3. Relation between the yield of benzothiophen compounds prepared using thiochroman and temperature. 20% ZnC12/AI,O3; space velocity (hr-1): ©--0-1; <>--1.4.
hydride ion; existence of a direct relation between the degree of conversion and catalyst acidity; absence of thermal conversions of the substances examined in the directions indicated; absence of the effect of inhibitors on conversions
247
Preparation of benzo~hiophen compounds from bieyelic sulphides TABLE 3. FORMATIOlq" OF BEI~ZOTHIOPHEI~T COMPOUNDS FROM THIOCHROMA~
10% ZnCl~/AliOs Yield, % theory
o£ T , °C
~CHs
350 400 450
0.1 1.4 04 1-4 0-1 1.4
6 2 8 6 19 10
4 2 9 6 19 13
11 5 21 13 52 29
1
1 4 1 12 5
"ii
2 1
60 54 71 60 82 73
(Table 1, e x p e r i m e n t in t h e presence of ionol); m i g r a t i o n o f s u b s t i t u e n t s a n d skeletal isomerization, which are n o t v e r y t y p i c a l of radical processes; t h e s e suggest t h a t a n ionic process t a k e s place on t h e c a t a l y s t s studied b y s y s t e m :
% ~
CII 3
~
/ CH~
%
1
CH3
s2-C
248
A.N.
KOREPANOV e~ a/.
Individual reactions and their sequence and the existence of hydride mobility for the compounds studied were confirmed experimentally [7-10]. It is possible that reactions take place partially or by a radical mechanism under the conditions applied. Experiments carried out with 2-methyl-2,3dihydrobenzothiophen and thioehroman in the presence of quartz indicate that at 400 ° and a space velocity of 0.1 hr -1 the first sulphide undergoes partial dehydrogenation; benzothiophen yield was 9~/o (Table 1). Dehydroisomerization of thiochroman at 450 ° and a space velocity of 0.1 hr -1 took place to a negligible extent, up to 3% (Fig. 2). At lower temperatures the radical process may be ignored (Table 1). Conversions of 2,2-dimethyl-2,3-dihydrobenzothiophen conform to the same relations as reactions of methyi-2,3-dihydrobenzothiophens and thioehroman and may be presented in the form of the ionic system:
tl a ~
+CH a 3
I
"/
+y c~q
"S" \CH3_ j
~,%,z,,s..~--c~ "
Thus, bicyclic sulphides of the 2,3-dihydrobenzothiophen and thiochroman series in the presence of catalysts with aprotonic acidity are converted to a mixture of benzothiophen compounds. Fairly high yields of the latter and the high selectivity of dehydrogenation and dehydro-isomerization, practically complete absence of separation of initial and end products to thiophenol and hydrogen sulphide, the comparative simplicity and ease of separating benzothiophens from other reaction products and separation of individual components, the possibility of selecting reaction conditions, in order to obtain one component enabled practical recommendations to be made relating to the use of bicyclic sulphide for preparing benzothiophens [11]. EXPERIMENTAL
2-Methyl-2,3-dihydrobenzothiophen and thiochroman were obtained at the same time from allylphenylsulphide [12]. The yield of the first sulphide was 80%, b.p. 97-99 ° (7 mmtIg); n~° 1.5925; d]° 1.0891. The yield of the second sulphide was 65%, b.p. 105-107 ° (7 mmHg); n~)° 1.6181; d| ° 1.1287. 3-Methyl-2,3-dihydrobenzothiophen was obtained by methods previously described [15]. Yield was 63%; b.p. 93-94 ° (6.5 mmtIg); n~ 1.5970; d] o 1.0964. Physical and chemical constants of compounds obtained agreed with results in the literature [12-15]. All compounds obtained were chromatographically pure. 2,2-Dimethyl-2,3-dihydrobenzothiophen was obtained by ring formation (2-
Preparation of benzothiophen compounds from bicyclic sulphides
249
methylallyl)-phenylsulphide over AlcOa at 300 ° and a space velocity of 0.2 hr -1 [16]. The catalysate consisted of 2,2-dimethyl-2,3-dihydrobenzothiophen (68%), thiophenol (9%), (2-methylpropenyl)-(16°/O), (2-methylpropyl)-(4°/O), (2-methylallyl)-phenylsulphides (1%) and 3-methylthiochroman (2%). The catalysate was dissolved in 25 g batches in an equal volume of n-heptane, the solution mixed for 0.5 hr with 5 ml 85% sulphuric acid. The acid layer was separated and agitation with a fresh acid sample repeated 5-6 times. The acid extracts were combined, diluted with water and extracted with heptane. These extracts were washed with water, dried using MgSO4 and after the elimination of solvent, distilled in vacuo. The product obtained contained 91~/o 2,2-dimethyl-2,3-dihydrobenzothiophen, 5 o (2-mcthylpropenyl)-phenylsulphide and 4% (2-methylpropyl)-sulphide. The yield of 2,2-dimethyl2,3-dihydrobenzothiophen was 41%. As a result of more prolonged purification (washing with acid for 2 hr) sulphide of 97~o purity* was obtained, b.p. 103106 ° (10 mmHg); n ~ 1.5706; d] 0 1.0388. Preparation of catalysts. Alumina. Industrial alumina was calcined in a muffle furnace for 5 hr at 500 °. 100 g calcined AlcOa was saturated with 50 ml distilled water and dried for 4 hr at 200 °. 20% zinc chloride on alumina. 20 g anhydrous ZnCl 2 was dissolved in 40 ml distilled water. 80 g AlcOa calcined at 500 ° was saturated with the solution obtained and dried at 200 °. 10% ZnCl2/A1203 was prepared b y a similar method. T A B L E 4. O V E R A L L A C I D I T Y AND SPECIFIC SURFACE OF CATALYST SAMPLES
Catalyst
Al~O8 HC1/AIzO, 10~o ZnCI~/AI203 20~o ZnClsAl2Os Aluminosilicate
Acidity mequiv n-butyl- Specific surface, m~/g amine/g catalyst 0"41 0"61 0"76 1"12 1"67
262 232 204 133 295
Alumina modified with hydrochloric acid. 34 g concentrated HCI (d~-l.17 gtcm a) was diluted with 30 ml distilled water: an acid solution was used to saturate 108 g A120 a calcined at 500 ° and dried for 4 hr at 200 °. Aluminosilicate catalyst. An industrial spherical aluminosilicate c a t a l y s t produced b y the Ufa catalyst plant was used for the study. The acidity of all catalysts was determined according to a previous description [17] and specific surface, b y another method [18]. Results are show~ in Table 4. * Due to mechanical loss, yield was reduced to 9~o.
250
A. N. KOREPANOVet al.
Catalytic transformations of sulphides were carried out in a continuous device, the velocity of transport gas (nitrogen) being 10 ml/min. Before the experiment the catalyst was heated for 2 hr in nitrogen at experimental temperature. A fresh catalyst sample was used in each experiment. Methods of analysis and separation of products of conversion were described previously [7, 19, 20]. Results are shown in Tables 1-3. SUMMARY
1. Bicyclic sulphides of 2,3-dihydrobenzothiophen and thiochroman series readily undergo dehydrogenation and dehydro-isomerization to compounds of benzothiophen series in the presence of catalysts with aprotonic acidity (A12Oa; 10, 20% ZnC12/A1203; aluminosilieate). Transformations of thioehroman take place with compression of the six-membered heterocycle. 2 . 2 0 % ZnCl~/Al~O8 is the optimum catalyst for aromatization of compounds of the 2,3-dihydrobenzothiophen series. Yields of bcnzothiophen compounds from mono-substituted bicyelie sulphides (2- and 3-mcthyl-2,3-dihydrobenzothiophens) reach 56-72% with a process selectivity of 85-96%. The yield of benzothiophen compounds from a di-substituted bicyelic sulphide (2,2dimethyl-2,3-dihydrobenzothiophen) exceeds 50% with a process selectivity of 75%. 3. 10% ZnCl~/A1203 is the optimum catalyst in aromatization of thiochroman. Benzothiophen yield exceeds 50% with a process selectivity of
82%. 4. The proposed catalytic method of obtaining benzothiophen compounds is simple and promising as bicyclic oil sulphides m a y be used as raw material for this purpose. \
REFERENCES
1. T. LESIAK, Roczn. Chemii 39, 939, 1965 2. S. I. ORADOVSKAYA, A. D. BERMAN and M. I. YANOVSKII, Neftekhimiya 11, 117, 1971 3. F. G. KHALIL', N. V. IMNADZE, T. A. DANILOVA and A. F. PLATE, Neftekhimiya 6, 472, 1966 4. S. KHUSHVAKHTOVA, T. A. DANILOVA and Ye. A. VIKTOROVA, Vestn. Mosk. un-ta, Khimiya, No. 1, 97, 1973 5. S. KHUSHVAKHTOVA, Kand. dis., MGU, 1970 6. A. N. KOREPANOV, T. A. DANILOVA and Ye. A. VIKTOROVA, Zh. organ, khlmii 9, 641, 1973 7. A. N. KOREPANOV, Kand. dis., MGU, 1974 8. G. I. BOLESTOVA, A. N. KOREPANOV, Z. N. PARNES and D. N. KURSANOV, Izv. AN SSSR, ser. khim., 2547. 1974 9. A. Ye. VIKTOROVA, A. A. FRE{~_~R, A. V. YEGOROV and L. M. PETROVA, KhGS, 141, 1973 10. L. M. KEDIK, Kand. dis., MGU, 1975
Preparation of benzothiophen compounds from bicyetie sulphides
251
11. Auth. Cert. U.S.S.R., 437 770, 30.07. 1974. Otkr., izobr., prom. obr. i toy. zn~ki, No. 28, 1974 12. H. KWART and E. R. EVANS, J. Organ. Chem. 31, 413, 1966 13. Ye. N. KARAULOVA, D. Sh. MEILANOVA and G. D. GAL'PERN, Zh. obshch. khimii 30, 3292, 1960 14. B. V. AIVAZOV, S. M. PETROVA, V. R. KHAIRULLINA and V. G. YAPRYNTSEVA, Fiziko-khimicheskiyo konstauty seroorganicheskikh soyedinenii (Physical and Chemical Constants of Organo-sulphur Compounds). Khimiya, Moscow, 1904 15. Ye. N. KARULOVA, D. Sh. MEILANOVA and G. D. GAL'PERN, Zh. obsheh, khlmli 29, 662, 1959 16. G. DZHAMALOVA, Kand. dis., MGU, 1972 17. O. JOHNSON, J. Phys. Chem. 59, 827, 1955 18. A. A. FREGER, Kand. dis., MGU, 1971 19. S. g~USHVAgHTOVA, A. N. KOREPANOV, T. A. DANILOVA and Ye. A. VIKTOROVA, Vestn. MGU, Khimiya 18, 574, 1972 20. Ta. DANILOVA and S. N. PETROV, l~eftekhimiya 14, 130, 1974
A STUDYwas made in this paper of dehydrogenation of 2- and 3-methyl-2,3-dihydrobenzothiophens and aehydro-isomerization of 2,2:dimethyl-2,3-dihydrobenzothiophen and thiochroman to corresponding benzothiophen compounds in the presence of catalyst with aprotonic acidity. TABLE 1.
FORMATION
OF
BENZOTHIOPHEN
COMPOUNDS
FROM
2-
A~D
3-METHY~L:2,3-DI-
HYDROBENZOTHIOPHENS
Space velocity 0.1 hr-~ Yield_____1%theo____~ Catalyst
•!P-
°c
~---7
I~'---'~
Overall
](x~F_~_CH,
N ~ / Y \ S / IN ~ / / \ { \ C I - I '
:Jbenzoth yield °f - Selec tivity,
N~//\S/[%i°phens'the°rY ]
%
2-Methyl -2, 3 -dihydrobenzothiophen 20% ZnCls/AliO 3 S a m e + 1% ionol Quartz AliO3 10% ZnC12/A1,O *
300
---
350
--
:
12
15 Traces
--
2 3
4
22 3 2o% zncl,/~,o,* 4 37 29 Quartz 400 3 6 AliO8 4 12 1 20% ZnCli/AliO s 11 15 14 3-Methyl:2,3-dihydrobenzothiophen 300 AlsOa 3 20% ZnCll/AlsO , -Traces 3 10% ZnC12/AI,O, 350 -3 9 20% ZnC1JAla0 , -14 19 i AlIOs 400 7 20% ZnC12/A120 s 13 20 20* * Found: 2% 2,3-dimethylbenzothiophen. ? Found: 3% 2.3-dtmethy]benzothiophen. --
18 0 4 25 72 9 17 44
85 84 0 80 85 89 100 61 76
3 3 12 33 7 56
100 50 65 67 61 96
Catalytic dehydrogenation of 2,3-dihydrobenzothiophen was previously carried out in the presence of chromium and copper applied on charcoal [1] and an alumina-chromium-beryllium catalyst [2]. It was shown subsequently * l~eftekhimiya 16, No. 6, 909-916, 1976. 242
Preparation of benzothiophen compounds from bicyclic sulphides
243
t h a t dehydrogenation of 2,3-dihydrobenzothiophen also takes place in the presence of alumlnosilicate having considerable aprotonic acidity [3] and on contact with 20% ZnC12]A1208, dehydro-isomerization of bicyclic sulphide (thiochroman) takes place with compression of the six-membered hetero-cycle, resulting, in a mixture of benzothiophen compounds [4, 5]. We used Al~O3, 10 and 20% ZnCl~/AI203 and an industrial spherical aluminosilicatc catalyst. The conversion of bicyelic sulphides was carried out in the temperature range of 300:-450 ° and at space velocities of 0.1-1.4 hr -1.
~Z % 88'
5
qO ,
12
F 2
4 ,i
1
C
%1
G
ZO,
#
0
300
i
350
f,°C q00
FIG. 1. Relation between the yield of benzothiophen compounds and temperature. 20~o ZnCls/A12Os; space velocity 0-1 hr-1; a--from 2-methyl-2,3-dihydrobenzothiophen; b--from 3-methyl-2,3-dihyctrobenzothiophen; c--from 2,2-dimethyl-2,3-d/hydrobenzothiophen. In Figs. 1-3: 1--benzothiophen; 2--2-methylbenzothiophen; 3--3-methylbenzothiophen; 4--2,3-dimethylbenzothiophen; 5--overall yield of benzothiophens; 6--process selectivity.
A. N. KOREPANOVet UL
244
Dehydrogenation of 2- and 3-methyl-2,3dihydrobenzothiophens took place on all catalyst samples under all kinds of reaction conditions. 2- and 3methylbenzothiophens and benzothiophens are the main products of the conversion of these sulphides. Benzothiophen was formed as a result of disproportionation of methylbenzothiophens [S]. In addition to benzothiophen, the catalysates contained methyl-2,3-dihydrobenzothiophen (isomer in relation to the initial products) and alkylbenzenes. It tollows from Table 1 and Fig. la and b that most satisfactory results were obtained in the presence of 20% ZnCl,/Al,O, at optimum temperatures of 350 and 375” using 2- and 3-methyl-2,3dihydrobenzothiophens, respectively for dehydrogenation on this catalyst. A shift in the maximum yield of benzothiophen compounds from 2-methyl-2,3dihydrobenzothiophen to low temperatures confirms an increased readiness to dehydrogenation. A reduction in the overall yields of benzothiophen compounds with an’ increase of temperature above the optimum value is due to an increase in the proportion of secondary processes (elimination of sulphur to form alkylbenzenes, deposition of products of condensation on the catalyst). Benzothiophen is an exception, the formation of which increases in a linear manner with an increase of temperature as a result of demethylation of homologues. Dehydrogenation takes place with a high degree of selectivity, which reaches 89 and 92% at optimum temperature for 2- and 3methyl-2,3-dihydrobenzothiophens, respectively (Fig. la and a). An increase in space velocity for sulphide reduces the yield of benzothiophens, process selectivity remaining practically unchanged. On contact with 10 and 20% ZnCl,/Al,OS at 300-400” and a space velocity of 0.1-03 hr-l 2,2-dimethyl-2,3-dihydrobenzothiophen is dehydro-isomerized mainly into 2,3dimethylbenzothiophen; the latter is partially demethylated into 2- and 3-methylbenzothiophens and benzothiophen (Table 2). In addition to benzothiophens, L-methylpropenyl phenyl sulphide (l-18%), 2,3dimethyl2,3-dihydrobenzothiophen* (1.6%) alkylbenzens (1-50/O) and thiophenol (l-3%) are formed. It follows from Table 2 that there is a direct relation between catalyst acidity and the overall yield of benzothiophen compounds. The effect of temperature on benzothiophen yield is shown in Fig. lc. The maximum yield of benzothiophens is 47-51%, independent of the variation of space velocity (O*l-0.8
hr-1).
The effect of space velocity on the overall yield of benzothiophens depends on experimental temperature: at 300 and 356’ its increase reduces yield; at 400” yield is practically independent of space velocity (Table 2), which is due to the low proportion of secondary processes. The maximum selectivity of the formation of benzothiophens reaches * IS O&
formed
at
300-350~.
Preparation of benzothiophen compounds from bieyelie sulphides
245
75% at 350 ° and at a low space velocity (0.1 hr-i) is practically independent of any further increase in temperature (Fig. lc). The main direction of conversion of thiochroman, on contact with 10 and 20% ZnCls/A1,O s or aluminosilieate, is dehydroisomerization, which products 2- and 3-methylbenzothiophens, benzothiophen and 2,3-dimethylbenzothioTABLE 2. F O R M A T I O N OF B E N Z O T H I O P H E N COMPOUNDS FROM 2 , 2 - D I M E T H Y L - 2 , 3 - D I H Y D R O BENZOTHIOPHEN
Yield, % theory
5
~
Catalyst
5 ~7
s
S
CHI
~; ~.~ I
kICI/A1203 to% ZnCld /AlIO3
300 350
Traces
0°1
--
300 350
0"1
300 300 300 350 350 350 400 400 400
0.1 0.4 0.8
Traces
Traces
Traces
3
3~
Traces
3 16
4 5( 18 5~
20% ZnCls/ /AlsO3
0.1
1
0.4 0.8 0.1 0.4 0.8
Traces 2 5 4 2
1 1 1 5 3
2 11 11 10
1
Traces 3 2 1
11 II 8
14 7 5 42 26 23 17 15 27
16 8 6 51 31 26 44 41 I 47
5( 4: 31 71 5: 5~ 7( 6~ 7:
phen. In the presence of A1203 isomerization of thiochroman to 2- and partly to 3-methyl-2,3-dihydrobenzothiophens is the prevailing process. The curve showing the dependence of the overall yield of b e n z o t h i o l ~ l ~ ~from thiochroman on catalyst acidity passes through the maximum wigh ~rerage acidity (Fig. 2). The ~emperature dependence of the overall yield of benzothiophens on the other hand follows a linear pattern (Fig. 3). Therefore, the maximum yield of benzothiophens from thiochroman was observed at 450 ° on contact with 10°/0 ZnC12/A120 a and was 52% with a selectivity of the process of 82% (Table 3, Fig. 2). During transformations of thiochroman in addition to benzothiophens, the following were formed under all conditions: alkylbenzenes (1-16%), thiophenol (1-6°/0),aad-2,.~ud 3-methyl-2,3-dihydrobenzothiophens. The amBunt
A. N. K o ~ . P ~ O V et al.
246
of the latter on contact with ZnCI~/AI~Oa, was negligible ( ~ 1%); in the presence of Al~03 on the other hand, it was 79%, the first isomer being predominant (74%); Selectivity of formation was 92%. An increase in space velocity reduced the yield of benzothiophens as a result of a lower degree of conversion of the initial sulphide (Table 3). It is significant that the qualitative composition of eatalysates obtained of three different sulphides (2- and 3-methyl-2,3-dihydrobenzothiophen and % 8O
8
~: qo 2o
!
0
0.5
l.O
1.5
Acidit~ , m-eTuiv.//9 FIe. 2. Relation between the yield of benzothiophen compounds prepared using thiochroman and the acidity of the catalyst. 450°; space velocity 0.1 hr -1. thioehroman) is the same. This suggests that conversions take place by a single mechanism. Conditions such as reaction only on contact with catalysts having aprotonic acidity (in the presence, for example, of A1203 modified with hydrochloric acid hardly any conversion takes place see Table 2) are as follows: presence on the catalyst surface of eentres capable of rupturing t h e % 80 I--
...I~°
.S ,,0~k1--°-" ..o-" ~...~ ..~0'~"
5
t
2° 1
JO0
5 -
350
6
o
zlO0
o
-2 a
Z¢50 t, °C
FIe. 3. Relation between the yield of benzothiophen compounds prepared using thiochroman and temperature. 20% ZnC12/AI,O3; space velocity (hr-1): ©--0-1; <>--1.4.
hydride ion; existence of a direct relation between the degree of conversion and catalyst acidity; absence of thermal conversions of the substances examined in the directions indicated; absence of the effect of inhibitors on conversions
247
Preparation of benzo~hiophen compounds from bieyelic sulphides TABLE 3. FORMATIOlq" OF BEI~ZOTHIOPHEI~T COMPOUNDS FROM THIOCHROMA~
10% ZnCl~/AliOs Yield, % theory
o£ T , °C
~CHs
350 400 450
0.1 1.4 04 1-4 0-1 1.4
6 2 8 6 19 10
4 2 9 6 19 13
11 5 21 13 52 29
1
1 4 1 12 5
"ii
2 1
60 54 71 60 82 73
(Table 1, e x p e r i m e n t in t h e presence of ionol); m i g r a t i o n o f s u b s t i t u e n t s a n d skeletal isomerization, which are n o t v e r y t y p i c a l of radical processes; t h e s e suggest t h a t a n ionic process t a k e s place on t h e c a t a l y s t s studied b y s y s t e m :
% ~
CII 3
~
/ CH~
%
1
CH3
s2-C
248
A.N.
KOREPANOV e~ a/.
Individual reactions and their sequence and the existence of hydride mobility for the compounds studied were confirmed experimentally [7-10]. It is possible that reactions take place partially or by a radical mechanism under the conditions applied. Experiments carried out with 2-methyl-2,3dihydrobenzothiophen and thioehroman in the presence of quartz indicate that at 400 ° and a space velocity of 0.1 hr -1 the first sulphide undergoes partial dehydrogenation; benzothiophen yield was 9~/o (Table 1). Dehydroisomerization of thiochroman at 450 ° and a space velocity of 0.1 hr -1 took place to a negligible extent, up to 3% (Fig. 2). At lower temperatures the radical process may be ignored (Table 1). Conversions of 2,2-dimethyl-2,3-dihydrobenzothiophen conform to the same relations as reactions of methyi-2,3-dihydrobenzothiophens and thioehroman and may be presented in the form of the ionic system:
tl a ~
+CH a 3
I
"/
+y c~q
"S" \CH3_ j
~,%,z,,s..~--c~ "
Thus, bicyclic sulphides of the 2,3-dihydrobenzothiophen and thiochroman series in the presence of catalysts with aprotonic acidity are converted to a mixture of benzothiophen compounds. Fairly high yields of the latter and the high selectivity of dehydrogenation and dehydro-isomerization, practically complete absence of separation of initial and end products to thiophenol and hydrogen sulphide, the comparative simplicity and ease of separating benzothiophens from other reaction products and separation of individual components, the possibility of selecting reaction conditions, in order to obtain one component enabled practical recommendations to be made relating to the use of bicyclic sulphide for preparing benzothiophens [11]. EXPERIMENTAL
2-Methyl-2,3-dihydrobenzothiophen and thiochroman were obtained at the same time from allylphenylsulphide [12]. The yield of the first sulphide was 80%, b.p. 97-99 ° (7 mmtIg); n~° 1.5925; d]° 1.0891. The yield of the second sulphide was 65%, b.p. 105-107 ° (7 mmHg); n~)° 1.6181; d| ° 1.1287. 3-Methyl-2,3-dihydrobenzothiophen was obtained by methods previously described [15]. Yield was 63%; b.p. 93-94 ° (6.5 mmtIg); n~ 1.5970; d] o 1.0964. Physical and chemical constants of compounds obtained agreed with results in the literature [12-15]. All compounds obtained were chromatographically pure. 2,2-Dimethyl-2,3-dihydrobenzothiophen was obtained by ring formation (2-
Preparation of benzothiophen compounds from bicyclic sulphides
249
methylallyl)-phenylsulphide over AlcOa at 300 ° and a space velocity of 0.2 hr -1 [16]. The catalysate consisted of 2,2-dimethyl-2,3-dihydrobenzothiophen (68%), thiophenol (9%), (2-methylpropenyl)-(16°/O), (2-methylpropyl)-(4°/O), (2-methylallyl)-phenylsulphides (1%) and 3-methylthiochroman (2%). The catalysate was dissolved in 25 g batches in an equal volume of n-heptane, the solution mixed for 0.5 hr with 5 ml 85% sulphuric acid. The acid layer was separated and agitation with a fresh acid sample repeated 5-6 times. The acid extracts were combined, diluted with water and extracted with heptane. These extracts were washed with water, dried using MgSO4 and after the elimination of solvent, distilled in vacuo. The product obtained contained 91~/o 2,2-dimethyl-2,3-dihydrobenzothiophen, 5 o (2-mcthylpropenyl)-phenylsulphide and 4% (2-methylpropyl)-sulphide. The yield of 2,2-dimethyl2,3-dihydrobenzothiophen was 41%. As a result of more prolonged purification (washing with acid for 2 hr) sulphide of 97~o purity* was obtained, b.p. 103106 ° (10 mmHg); n ~ 1.5706; d] 0 1.0388. Preparation of catalysts. Alumina. Industrial alumina was calcined in a muffle furnace for 5 hr at 500 °. 100 g calcined AlcOa was saturated with 50 ml distilled water and dried for 4 hr at 200 °. 20% zinc chloride on alumina. 20 g anhydrous ZnCl 2 was dissolved in 40 ml distilled water. 80 g AlcOa calcined at 500 ° was saturated with the solution obtained and dried at 200 °. 10% ZnCl2/A1203 was prepared b y a similar method. T A B L E 4. O V E R A L L A C I D I T Y AND SPECIFIC SURFACE OF CATALYST SAMPLES
Catalyst
Al~O8 HC1/AIzO, 10~o ZnCI~/AI203 20~o ZnClsAl2Os Aluminosilicate
Acidity mequiv n-butyl- Specific surface, m~/g amine/g catalyst 0"41 0"61 0"76 1"12 1"67
262 232 204 133 295
Alumina modified with hydrochloric acid. 34 g concentrated HCI (d~-l.17 gtcm a) was diluted with 30 ml distilled water: an acid solution was used to saturate 108 g A120 a calcined at 500 ° and dried for 4 hr at 200 °. Aluminosilicate catalyst. An industrial spherical aluminosilicate c a t a l y s t produced b y the Ufa catalyst plant was used for the study. The acidity of all catalysts was determined according to a previous description [17] and specific surface, b y another method [18]. Results are show~ in Table 4. * Due to mechanical loss, yield was reduced to 9~o.
250
A. N. KOREPANOVet al.
Catalytic transformations of sulphides were carried out in a continuous device, the velocity of transport gas (nitrogen) being 10 ml/min. Before the experiment the catalyst was heated for 2 hr in nitrogen at experimental temperature. A fresh catalyst sample was used in each experiment. Methods of analysis and separation of products of conversion were described previously [7, 19, 20]. Results are shown in Tables 1-3. SUMMARY
1. Bicyclic sulphides of 2,3-dihydrobenzothiophen and thiochroman series readily undergo dehydrogenation and dehydro-isomerization to compounds of benzothiophen series in the presence of catalysts with aprotonic acidity (A12Oa; 10, 20% ZnC12/A1203; aluminosilieate). Transformations of thioehroman take place with compression of the six-membered heterocycle. 2 . 2 0 % ZnCl~/Al~O8 is the optimum catalyst for aromatization of compounds of the 2,3-dihydrobenzothiophen series. Yields of bcnzothiophen compounds from mono-substituted bicyelie sulphides (2- and 3-mcthyl-2,3-dihydrobenzothiophens) reach 56-72% with a process selectivity of 85-96%. The yield of benzothiophen compounds from a di-substituted bicyelic sulphide (2,2dimethyl-2,3-dihydrobenzothiophen) exceeds 50% with a process selectivity of 75%. 3. 10% ZnCl~/A1203 is the optimum catalyst in aromatization of thiochroman. Benzothiophen yield exceeds 50% with a process selectivity of
82%. 4. The proposed catalytic method of obtaining benzothiophen compounds is simple and promising as bicyclic oil sulphides m a y be used as raw material for this purpose. \
REFERENCES
1. T. LESIAK, Roczn. Chemii 39, 939, 1965 2. S. I. ORADOVSKAYA, A. D. BERMAN and M. I. YANOVSKII, Neftekhimiya 11, 117, 1971 3. F. G. KHALIL', N. V. IMNADZE, T. A. DANILOVA and A. F. PLATE, Neftekhimiya 6, 472, 1966 4. S. KHUSHVAKHTOVA, T. A. DANILOVA and Ye. A. VIKTOROVA, Vestn. Mosk. un-ta, Khimiya, No. 1, 97, 1973 5. S. KHUSHVAKHTOVA, Kand. dis., MGU, 1970 6. A. N. KOREPANOV, T. A. DANILOVA and Ye. A. VIKTOROVA, Zh. organ, khlmii 9, 641, 1973 7. A. N. KOREPANOV, Kand. dis., MGU, 1974 8. G. I. BOLESTOVA, A. N. KOREPANOV, Z. N. PARNES and D. N. KURSANOV, Izv. AN SSSR, ser. khim., 2547. 1974 9. A. Ye. VIKTOROVA, A. A. FRE{~_~R, A. V. YEGOROV and L. M. PETROVA, KhGS, 141, 1973 10. L. M. KEDIK, Kand. dis., MGU, 1975
Preparation of benzothiophen compounds from bicyetie sulphides
251
11. Auth. Cert. U.S.S.R., 437 770, 30.07. 1974. Otkr., izobr., prom. obr. i toy. zn~ki, No. 28, 1974 12. H. KWART and E. R. EVANS, J. Organ. Chem. 31, 413, 1966 13. Ye. N. KARAULOVA, D. Sh. MEILANOVA and G. D. GAL'PERN, Zh. obshch. khimii 30, 3292, 1960 14. B. V. AIVAZOV, S. M. PETROVA, V. R. KHAIRULLINA and V. G. YAPRYNTSEVA, Fiziko-khimicheskiyo konstauty seroorganicheskikh soyedinenii (Physical and Chemical Constants of Organo-sulphur Compounds). Khimiya, Moscow, 1904 15. Ye. N. KARULOVA, D. Sh. MEILANOVA and G. D. GAL'PERN, Zh. obsheh, khlmli 29, 662, 1959 16. G. DZHAMALOVA, Kand. dis., MGU, 1972 17. O. JOHNSON, J. Phys. Chem. 59, 827, 1955 18. A. A. FREGER, Kand. dis., MGU, 1971 19. S. g~USHVAgHTOVA, A. N. KOREPANOV, T. A. DANILOVA and Ye. A. VIKTOROVA, Vestn. MGU, Khimiya 18, 574, 1972 20. Ta. DANILOVA and S. N. PETROV, l~eftekhimiya 14, 130, 1974