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Catalytic cyclodimerization of piperylene
100
V. S. SHAMA~EV et al.
9. L. G. ANTONOVA, and A. I. KRASIL'SHCHIKOV, Zh. fiz. khimii 41, 2230, 1967 10. R. DUS', Vses. konf. po mekhanizmu geterogenno-kataliticheskikh reaktsii (All-Uifion Conference on the Mechanism of Heterogeneous-Catalytic :Reactions). Moscow, 1974, prepr. No. 84 11. P. W. SELW0OD, J. Catalysis 42, 148, 1976 12. D. V. SOKOLOVSKII and Ya. A. DORFMAN, Koordinatsiya igidrirovaniye na metallakh, AJma Ata, 1975 13. P. DEBYE, Physik Z. 21, 178, 1920; 22, 302, 1921 14. C. G. LE FEVRE and R. J. W. LE FEVRE, J. Chem. Soc., 483, 1936 15. V. A. PAL'M, Vvedeniye v teoreticheskuyu organicheskuyu khimiyu (Introduction into Theoretical Organic Chemistry). Vysshaya shkola, Moscow, 1974 16. E. AMIS, Vliyaniye rastvoriteIya na skorost' i mekhanizm khimicheskikh reaktsii (Effect of Solvent On the :Rate and Mechanism of Chemical :Reactions). Mir, Moscow, 1968
CATALYTIC CYCLODIMERIZATION OF PIPERYLENE* V. S. SHAM.AYEV,L. P. STEPAI~OVAL. V. SH~ELEV, A. N. RATOV A~D G.KH. RICHMOND State Scientifc Research Institute of the Paint and Varnish Industry (Received 6 October 1976)
CYCLODIMERIZATION of piperylene on composite nickel catalysts in the presence o f organo-phosphorus ligands results m a i n l y in d i m e t h y l c y c l o - o c t a - l , 5 - d i e n e isomers [1-3]. Prospects of the practical application of the p r o d u c t s f o r m e d account for the considerable interest a t t a c h e d to the s t u d y of features o f dimerization of piperylene. The selection of a reducing agent of transition metal compounds is i m p o r t a n t . T h e d i e t h y l e t h o x y a l u m i n i u m [1] and triethylalumininm [2] used for these purposes are unsuitable in view of p y r o p h o r i c properties. Authors of a previous p a p e r [3] used more appropriate s y n t h e t i c reducing agents: diethylamino-aluminiumdiethyl, tris-(3-methyl-4,6-heptadienyl) aluminium and perhydro-9v-aluminophenolene. Dimerization of piperylene was carried out in a n inert solvent in all well k n o w n investigations. According to previous papers [1] and [3] isomers of 3,7-dimethylcyclo-octa-l,5diene (3,7-DMCOD) are formed as a result of dimerization, while the 3,4-dimethylcyclo-octa-l,5-diene (3,4-DMCOD) isomer is f o r m e d in smaller quantities, i n d e p e n d e n t of the ratio of the vis/trans-forms of pipery]ene in the initial mixture. W e studied dimerization of piperylene with various ratios of isomer forms u n d e r conditions close to [1] a n d [3]. I n c o n t r a s t to well-known studies, we e x a m i n e d cyclodimerization of piperylene b y the action of nickel complexes * Neftekhimiya 17, No. 3, 401-405, 1977.
Catalytic cyclodimerization of piperylene
101
without using a solvent, while tri-isobutyluminium produced in this country was used as reducing agent as it does not ignite in air. As a result of investigations it was established t h a t changing the ratio of isomer forms of piperylene in the mixture influences conversion and the selectivity of formation of end products (Table). EFFECT
OF THE
RATIO
CONVERSION
Trans, cis
OF ISOMER
AND
THE
Piperylene eonersion,
FORMS
OF PIPERYLENE
SELECTIVITY
CsH10(CHs)~
OF FORMATION
IN THE
MIXTURE
OF REACTION
Selectivity, % C6Hs(CHs) (CH=CH--CHs)
ON
PIPERYLENE
PRODUCTS
oligomers
85/15
26"9 21"3
58-3 58-2
5-7 7.8
36"0 34"0
54/46
25"5 22"4
65'6 66"0
10.7 6.3
23'7 27"7
38/62
77"5 74'5 75'0
73-5 76'2 76"9
14.3 11.8 10.6
12"2 12"0 13"5
14/86
81'3 81-3 84"0
70.8 74.0 70.0
17-8 15.2 18.0
11"4 10'8 12"0
* Isomers of methylpropenylcyclohexene. I t was found t h a t the composition of eight-membered cyclodimers is characterized by three chromatographic peaks two of which have similar yield times and the third differs markedly from the first two. In contrast to a previous study [3] it was found t h a t ~he ratio of DMCOD isomers varies according to the composition of the initial mixture of cis-/trans-piperylene. On using an initial mixture enriched with trans-piperylene, the content of isomer, corresponding to the second chromatographic peak increased in reaction products with a reduction of the first and third peak. An increase in cis-piperylene content in the initial mixture increased the first and third peaks (Figure). To explain experimental facts observed, the three fractions of eight-membered cyclodimers, corresponding to peaks 1-3 separated by preparatory methods, were examined by PMR spectroscopy. The first fraction appeared to be the mixture of two isomers, since two doublets of CH a protons were observed in the PMR spectrum, which differed as regards chemical shift with an intensity ratio of 7:3. One CH a doublet was observed in the spectrum of the second fraction, the chemical shift of protons of this group coinciding with one of the doublets in the spectrum of the first fraction. A comparison of PMR spectra of the first and second fraction and results described previously [3]
,102
V.S. Sm~Y~v
et a l .
suggest t h a t p r o d u c t s corresponding t o c h r o m a t o g r a p h i c peaks Nos. 1 a n d 2 are isomers of 3,7-DMCOD, in one of which m e t h y l groups o c c u p y a x i a l positions (~=-0.95 mln-1), in the other, equatorial positions (~-----1.03 mln-1). An isomer corresponding to the t h i r d c h r o m a t o g r a p h i c peak was also isolated. Its s t r u c t u r e was established b y the m e t h o d of double resonance. Chemical shifts of methine protons were defined more a c c u r a t e l y b y recording spectra u n d e r conditions of YNDOR. On isolating spin-spin interactions it was f o u n d t h a t the signal of methine protons is isolated from m e t h y l into a b r o a d doublet ( I ~ 4.5 c/s), which is due to vicinal interaction with olefin protons; the broadening of c o m p o n e n t s is due to the existence of an allyl constant I ~- 1.2 c/s. Since o t h e r interactions do not take place on being isolated from methyls it m a y be concluded t h a t protons combined with carbon atoms in positions 3 a n d 4 are equivalent magnetic p r o t o n s of methine groups. Isolating o t h e r
1 2
J
~Chromatographie curves of dimethyleyclo-oetadieno isomers formed with different ratios o f c i s - and t r a n s - i s o m e r s o f piperylene in the initial mixture: a - - c i s : t r a n s = 63: 37; b - - c i s : t r a n s = 19 : 81; 1 -- 3.7-dimethylcyclo-octa-1,5-diene with substituents in axial positions; 2 -- 3,7-dimothyleyclo-octa-l,5-diene with substituents in equatorial positions; 3 -- 3,4-dimethylcyclo-octa-l,5-diono with substituonts in axial positions.
spin-spin interactions also confirmed t h a t the isomer corresponding to the t h i r d p e a k is 3,4-DMCOD. This was also p r o v e d b y a more noticeable difference in chemical shifts of olefin protons, observed in the s p e c t r u m of this isomer,
Catalytic cyclodimerization of piperylene
103
compared with spectra of fractions, corresponding to the first two peaks and concerning 3,7-DMCOD isomers. Signals of olefin protons appear in the narrower region in spectra of the latter. This conclusion is in agreement with earlier results [3], in which the structure of 3,4-DMCOD--an isomer with the longest yield time - - w a s confirmed b y ozonolysis of the dimer resulting in the formation of dimethyl succinic and succinic acids. Possible conformations of DMCOD were examined [3] and " b o a t " ' conformation with two methyl groups in equatorial positions was attibuted to the 3,4-DI~ICOD formed. A study of the P M R spectrum of 3,4-DI~ICOD obtained in our experiments, which agrees with the spectrum of this product [3], suggests another conclusion. It follows from a study of isomer conformations using molecular models (Dryding) that methine protons in equatorial positions in the DMCOD molecule are outside the plane of olefin bonds, and their signals are displaced to the weak field in relation to signals of methine protons in axial positions, which are situated under the plane of double bonds. Bearing this in mind it follows from spectra that 3,4-DMCOD formed in experiments of dimerization of piperylene, is an isomer with methyl groups in axial positions. Since it may be expected that protons of CIta groups are repelled in the boat conformation, a "chair" conformation is preferred in this case, in which methyl groups are at a distance from each other (torsional angle z ~ 180 °) and are unable to interact. Comparing chemical shift of methine protons, which were also more accurately defined according to spectra of INDOR, it may be concluded that the isomer with a shorter yield time is 3,7-DMCOD in spectra of products corresponding to chromatographic peaks 1 and 2, with two methyl groups in axial positions, while the isomer corresponding to the second peak is 3,7-DI~COD with equatorial methyl groups. The equatorial position of CH 3 groups in the second isomer is in agreement with the displacement of proton doublet of CH 3 groups in the spectrum to the weak field (5----1.03 mln-1), compared with the position of signals of axial CH3 groups. For an isomer with axial methyl groups the chair conformation is preferred, whereas for an isomer with equatorial methyl groups chair and boat conformations are equivalent. Results of the structure of DMCOD isomers formed are in satisfactory agreement with results showing the dependence of the composition of products formed on the ratio of cis-/trans-piperylene in the initial mixture. Since the formation of 3,4- and 3,7-DMCOD with CH 3 groups in axial positions may be presented as dimerization of two cis-piperylene molecules, the increased yield of 3,4- and 3,7-DI~COD with axial CHa groups becomes clear on increasing the cis-piperylene content of the initial mixture. Similarly, the formation of an isomer with equatorial methyl groups is shown as dimerization of two trans-piperylene molecules, which is in agreement with the increased yield of 3,7-DMCOD with equatorial methyl groups (peak 2) on increasing the transpiperylene content in the initial mixture.
104
V.S.
SHAMAYEY e t a [ .
EXPERIMENTAL
Piperylene of a purity of not less than 99.2% was used. Hydrocarbon mixtures were analysed in a Tsvet-1 chromatograph, with a flame-ionization detector, column length being 3m; 15~o polyethyleneglycol adipate on chromosorb A was used and nitrogen was the carrier gas. Preparatory separation was carried out in a Tsvet-3 chromatograph, column length being 3 m, and filler, the same. A flame-ionization detector was used and nitrogen was the carrier gas. PMR spectra were recorded in a Varian NA-100D spectrometer in CCIa and CsH 6 and tetramethylsilane was the internal standard. I R spectra were obtained in a UR-10 Zeiss spectrophotometer and mass-spectra, in an MKh-1303 device. Cyclodimerization of piperylene. 0.0078 mole Ni (acac)2, 0.0078 mole tris(o-biphenyl)-phosphite, 2.0 mole piperylene were introduced in an autoclave provided with a stirrer, under argon. The autoclave was cooled to --10-(--5) ° and then 0.0348 mole tri-isobutylaluminium added while stirring constantly. The autoclave was kept at 100 ° for 5 hr, then cooled to room temperature and its contents transferred into a flask for distillation. Unreacted piperylene was distilled at a temperature of 42-44 ° under atmospheric pressure and the cyclodimers formed were distilled at 36-42°/2 mm. Piperylene dimers isolated by preparatory chromatography had the following characteristics. 3,7-Dimethylcyclo-octa-l,5-diene (1). B.p. 36°/2mm, n~°=1.4812, IRS: (v, cm-1): 720, 1665 (cis-HC=CH), 1380, 1450 (CH3). PMR (J, m]n-1): in CC14--1-00 (611 C113, I = 7 c/s), 2.07-2.86 (4H CH2, 21{ CI-I), 5.17 (4111C H = = C t t ) ; in C61-I6--0"92 (CI-I3) , 2-07-2.28 (CH2), 2.78 (CH), 5.27 (HC=); m/e 136. 3,7-Dimethylcyclo-octa-l,5-diene (2). B.p. 36°/2mm, n~°=1.4877, IRS (v, cm-1): 720, 1650 (cis-HC=CH), 1380, 1450 (C1{s). PMR (J, mln-1): in CC14--1-03 (6111CH.~, 1-----7 c/s), 2.0 (2H CH), 2.2-2.23 (4tt CH2) 5.32 (4I-I HC----); in C6116 0.97 (CHs), 2.21-2.27 (2H CH), 2.13-2.30 (4111 CH2); m/e 136. ~0 3,4-Dimethylcyclo-octa-l,5-diene (3). B.p. 40°/2mm, n/~=1,4888, IRS (v, cm-1): 720, 1650 (cis-1{C~--CH), 1380, 1450 (CH3). PMR (g, mln-~): in CCl4--0.95 (6tt CH3), 2.08--2.62 (4H CH2), 2.94 (21t CH), 5.17--5.43 (4H 11C~-); in Ce1{e 0.92 (C1{3), 1-97--2.52 (C1{2), 2.91 (Ctt), m/e 136. SUMMARY
1. A study was made of catalytic cyclodimerization of piperylene on Ni (acac)2-- P(OC6H4-- OC8H5) s- (C4H9) 3 A] at a temperature of 100°C. 2. Piperylene conversion and the selectivity of formation of end products depend on the ratio of isomeric forms of piperylene in the initial mixture. When the mixture is enriched with ci8-piperylene, 3,4- and 3,7-dimethylcyclo-l,5-octadienes with substituents in the axial positions, are formed. When the initial mixture is enriched with trans-piperylene 3,7-dimethylcyclo-
Molybdenum disulphide
105
octa-l,5-diene with substituents in the equatorial positions predominates reaction products. 3. The structure of dimethylcyclooctadiene isomers formed is confirmed by PMR and I R spectroscopy. REFERENCES
1. German Pat. 1140569, 1962; Chem. Abstrs 58, 11214, 1963 2. U.S.A. Pat. 3446862, 1969; ]:tZ hKhim. 12N, 2112, 1970 3. U. M. DZHE1KILEV, G. Ye. IVANOV and G. A. TOLSTLKOV,Neftekhimiya 15, 819, 1975
MOLYBDENUM DISULPHIDE AS HETEROGENEOUS INHIBITOR IN OXIDATION OF HYDROCARBONS* G. I. KOVAL~V, L. D. GOGITIDZE, V. I. KU~A~OVA, Yu. N. DYSHLEVSKII and Y~. T. DENISOV Institute of Chemical Physics, U.S.S.R. Academy of Sciences (Received 10 November 1975)
VARIOUS organic compounds soluble in hydrocarbons, which are homogeneous inhibitors are now used as inhibitors of oxidation of hydrocarbons. Heterogeneous inhibitors are at first sight of low activity in liquid phase in view of slow diffusion and comparatively rapid recombination of radicals. On the other hand heterogeneous inhibitors, semiconductors in particular, according to the semiconductor theory of catalysis [1], may form active centres on the surface and under given conditions m a y cause both repeated loss of chains (inhibition) and repeated formation of chains (catalysis) on an active centre. The inhibiting action of metal oxides on liquid-phase oxidation of hydrocarbons [2] has been noted in the literature. Using molybdenum disulphide we found an interesting case of repeated chain rupture on the surface of a heterogeneous inhibitor. Kinetic relations of inhibition of molybdenum disulphide also appeared to be quite different from those of homogeneous inhibitors. METHODS
Oxidation of hydrocarbons was studied in a gas,~metric static apparatus at a temperature of 125°C. A cylindrical glass reactor 30 mm in diameter and 120 cm s in volume provided with a special stirrer was used. The stirrer rotated a t a speed of 10-20 rev./sec to ensure even distribution of molybdenum di* Neftekhimiya 17, No. 3, 438-443, 1977.
V. S. SHAMA~EV et al.
9. L. G. ANTONOVA, and A. I. KRASIL'SHCHIKOV, Zh. fiz. khimii 41, 2230, 1967 10. R. DUS', Vses. konf. po mekhanizmu geterogenno-kataliticheskikh reaktsii (All-Uifion Conference on the Mechanism of Heterogeneous-Catalytic :Reactions). Moscow, 1974, prepr. No. 84 11. P. W. SELW0OD, J. Catalysis 42, 148, 1976 12. D. V. SOKOLOVSKII and Ya. A. DORFMAN, Koordinatsiya igidrirovaniye na metallakh, AJma Ata, 1975 13. P. DEBYE, Physik Z. 21, 178, 1920; 22, 302, 1921 14. C. G. LE FEVRE and R. J. W. LE FEVRE, J. Chem. Soc., 483, 1936 15. V. A. PAL'M, Vvedeniye v teoreticheskuyu organicheskuyu khimiyu (Introduction into Theoretical Organic Chemistry). Vysshaya shkola, Moscow, 1974 16. E. AMIS, Vliyaniye rastvoriteIya na skorost' i mekhanizm khimicheskikh reaktsii (Effect of Solvent On the :Rate and Mechanism of Chemical :Reactions). Mir, Moscow, 1968
CATALYTIC CYCLODIMERIZATION OF PIPERYLENE* V. S. SHAM.AYEV,L. P. STEPAI~OVAL. V. SH~ELEV, A. N. RATOV A~D G.KH. RICHMOND State Scientifc Research Institute of the Paint and Varnish Industry (Received 6 October 1976)
CYCLODIMERIZATION of piperylene on composite nickel catalysts in the presence o f organo-phosphorus ligands results m a i n l y in d i m e t h y l c y c l o - o c t a - l , 5 - d i e n e isomers [1-3]. Prospects of the practical application of the p r o d u c t s f o r m e d account for the considerable interest a t t a c h e d to the s t u d y of features o f dimerization of piperylene. The selection of a reducing agent of transition metal compounds is i m p o r t a n t . T h e d i e t h y l e t h o x y a l u m i n i u m [1] and triethylalumininm [2] used for these purposes are unsuitable in view of p y r o p h o r i c properties. Authors of a previous p a p e r [3] used more appropriate s y n t h e t i c reducing agents: diethylamino-aluminiumdiethyl, tris-(3-methyl-4,6-heptadienyl) aluminium and perhydro-9v-aluminophenolene. Dimerization of piperylene was carried out in a n inert solvent in all well k n o w n investigations. According to previous papers [1] and [3] isomers of 3,7-dimethylcyclo-octa-l,5diene (3,7-DMCOD) are formed as a result of dimerization, while the 3,4-dimethylcyclo-octa-l,5-diene (3,4-DMCOD) isomer is f o r m e d in smaller quantities, i n d e p e n d e n t of the ratio of the vis/trans-forms of pipery]ene in the initial mixture. W e studied dimerization of piperylene with various ratios of isomer forms u n d e r conditions close to [1] a n d [3]. I n c o n t r a s t to well-known studies, we e x a m i n e d cyclodimerization of piperylene b y the action of nickel complexes * Neftekhimiya 17, No. 3, 401-405, 1977.
Catalytic cyclodimerization of piperylene
101
without using a solvent, while tri-isobutyluminium produced in this country was used as reducing agent as it does not ignite in air. As a result of investigations it was established t h a t changing the ratio of isomer forms of piperylene in the mixture influences conversion and the selectivity of formation of end products (Table). EFFECT
OF THE
RATIO
CONVERSION
Trans, cis
OF ISOMER
AND
THE
Piperylene eonersion,
FORMS
OF PIPERYLENE
SELECTIVITY
CsH10(CHs)~
OF FORMATION
IN THE
MIXTURE
OF REACTION
Selectivity, % C6Hs(CHs) (CH=CH--CHs)
ON
PIPERYLENE
PRODUCTS
oligomers
85/15
26"9 21"3
58-3 58-2
5-7 7.8
36"0 34"0
54/46
25"5 22"4
65'6 66"0
10.7 6.3
23'7 27"7
38/62
77"5 74'5 75'0
73-5 76'2 76"9
14.3 11.8 10.6
12"2 12"0 13"5
14/86
81'3 81-3 84"0
70.8 74.0 70.0
17-8 15.2 18.0
11"4 10'8 12"0
* Isomers of methylpropenylcyclohexene. I t was found t h a t the composition of eight-membered cyclodimers is characterized by three chromatographic peaks two of which have similar yield times and the third differs markedly from the first two. In contrast to a previous study [3] it was found t h a t ~he ratio of DMCOD isomers varies according to the composition of the initial mixture of cis-/trans-piperylene. On using an initial mixture enriched with trans-piperylene, the content of isomer, corresponding to the second chromatographic peak increased in reaction products with a reduction of the first and third peak. An increase in cis-piperylene content in the initial mixture increased the first and third peaks (Figure). To explain experimental facts observed, the three fractions of eight-membered cyclodimers, corresponding to peaks 1-3 separated by preparatory methods, were examined by PMR spectroscopy. The first fraction appeared to be the mixture of two isomers, since two doublets of CH a protons were observed in the PMR spectrum, which differed as regards chemical shift with an intensity ratio of 7:3. One CH a doublet was observed in the spectrum of the second fraction, the chemical shift of protons of this group coinciding with one of the doublets in the spectrum of the first fraction. A comparison of PMR spectra of the first and second fraction and results described previously [3]
,102
V.S. Sm~Y~v
et a l .
suggest t h a t p r o d u c t s corresponding t o c h r o m a t o g r a p h i c peaks Nos. 1 a n d 2 are isomers of 3,7-DMCOD, in one of which m e t h y l groups o c c u p y a x i a l positions (~=-0.95 mln-1), in the other, equatorial positions (~-----1.03 mln-1). An isomer corresponding to the t h i r d c h r o m a t o g r a p h i c peak was also isolated. Its s t r u c t u r e was established b y the m e t h o d of double resonance. Chemical shifts of methine protons were defined more a c c u r a t e l y b y recording spectra u n d e r conditions of YNDOR. On isolating spin-spin interactions it was f o u n d t h a t the signal of methine protons is isolated from m e t h y l into a b r o a d doublet ( I ~ 4.5 c/s), which is due to vicinal interaction with olefin protons; the broadening of c o m p o n e n t s is due to the existence of an allyl constant I ~- 1.2 c/s. Since o t h e r interactions do not take place on being isolated from methyls it m a y be concluded t h a t protons combined with carbon atoms in positions 3 a n d 4 are equivalent magnetic p r o t o n s of methine groups. Isolating o t h e r
1 2
J
~Chromatographie curves of dimethyleyclo-oetadieno isomers formed with different ratios o f c i s - and t r a n s - i s o m e r s o f piperylene in the initial mixture: a - - c i s : t r a n s = 63: 37; b - - c i s : t r a n s = 19 : 81; 1 -- 3.7-dimethylcyclo-octa-1,5-diene with substituents in axial positions; 2 -- 3,7-dimothyleyclo-octa-l,5-diene with substituents in equatorial positions; 3 -- 3,4-dimethylcyclo-octa-l,5-diono with substituonts in axial positions.
spin-spin interactions also confirmed t h a t the isomer corresponding to the t h i r d p e a k is 3,4-DMCOD. This was also p r o v e d b y a more noticeable difference in chemical shifts of olefin protons, observed in the s p e c t r u m of this isomer,
Catalytic cyclodimerization of piperylene
103
compared with spectra of fractions, corresponding to the first two peaks and concerning 3,7-DMCOD isomers. Signals of olefin protons appear in the narrower region in spectra of the latter. This conclusion is in agreement with earlier results [3], in which the structure of 3,4-DMCOD--an isomer with the longest yield time - - w a s confirmed b y ozonolysis of the dimer resulting in the formation of dimethyl succinic and succinic acids. Possible conformations of DMCOD were examined [3] and " b o a t " ' conformation with two methyl groups in equatorial positions was attibuted to the 3,4-DI~ICOD formed. A study of the P M R spectrum of 3,4-DI~ICOD obtained in our experiments, which agrees with the spectrum of this product [3], suggests another conclusion. It follows from a study of isomer conformations using molecular models (Dryding) that methine protons in equatorial positions in the DMCOD molecule are outside the plane of olefin bonds, and their signals are displaced to the weak field in relation to signals of methine protons in axial positions, which are situated under the plane of double bonds. Bearing this in mind it follows from spectra that 3,4-DMCOD formed in experiments of dimerization of piperylene, is an isomer with methyl groups in axial positions. Since it may be expected that protons of CIta groups are repelled in the boat conformation, a "chair" conformation is preferred in this case, in which methyl groups are at a distance from each other (torsional angle z ~ 180 °) and are unable to interact. Comparing chemical shift of methine protons, which were also more accurately defined according to spectra of INDOR, it may be concluded that the isomer with a shorter yield time is 3,7-DMCOD in spectra of products corresponding to chromatographic peaks 1 and 2, with two methyl groups in axial positions, while the isomer corresponding to the second peak is 3,7-DI~COD with equatorial methyl groups. The equatorial position of CH 3 groups in the second isomer is in agreement with the displacement of proton doublet of CH 3 groups in the spectrum to the weak field (5----1.03 mln-1), compared with the position of signals of axial CH3 groups. For an isomer with axial methyl groups the chair conformation is preferred, whereas for an isomer with equatorial methyl groups chair and boat conformations are equivalent. Results of the structure of DMCOD isomers formed are in satisfactory agreement with results showing the dependence of the composition of products formed on the ratio of cis-/trans-piperylene in the initial mixture. Since the formation of 3,4- and 3,7-DMCOD with CH 3 groups in axial positions may be presented as dimerization of two cis-piperylene molecules, the increased yield of 3,4- and 3,7-DI~COD with axial CHa groups becomes clear on increasing the cis-piperylene content of the initial mixture. Similarly, the formation of an isomer with equatorial methyl groups is shown as dimerization of two trans-piperylene molecules, which is in agreement with the increased yield of 3,7-DMCOD with equatorial methyl groups (peak 2) on increasing the transpiperylene content in the initial mixture.
104
V.S.
SHAMAYEY e t a [ .
EXPERIMENTAL
Piperylene of a purity of not less than 99.2% was used. Hydrocarbon mixtures were analysed in a Tsvet-1 chromatograph, with a flame-ionization detector, column length being 3m; 15~o polyethyleneglycol adipate on chromosorb A was used and nitrogen was the carrier gas. Preparatory separation was carried out in a Tsvet-3 chromatograph, column length being 3 m, and filler, the same. A flame-ionization detector was used and nitrogen was the carrier gas. PMR spectra were recorded in a Varian NA-100D spectrometer in CCIa and CsH 6 and tetramethylsilane was the internal standard. I R spectra were obtained in a UR-10 Zeiss spectrophotometer and mass-spectra, in an MKh-1303 device. Cyclodimerization of piperylene. 0.0078 mole Ni (acac)2, 0.0078 mole tris(o-biphenyl)-phosphite, 2.0 mole piperylene were introduced in an autoclave provided with a stirrer, under argon. The autoclave was cooled to --10-(--5) ° and then 0.0348 mole tri-isobutylaluminium added while stirring constantly. The autoclave was kept at 100 ° for 5 hr, then cooled to room temperature and its contents transferred into a flask for distillation. Unreacted piperylene was distilled at a temperature of 42-44 ° under atmospheric pressure and the cyclodimers formed were distilled at 36-42°/2 mm. Piperylene dimers isolated by preparatory chromatography had the following characteristics. 3,7-Dimethylcyclo-octa-l,5-diene (1). B.p. 36°/2mm, n~°=1.4812, IRS: (v, cm-1): 720, 1665 (cis-HC=CH), 1380, 1450 (CH3). PMR (J, m]n-1): in CC14--1-00 (611 C113, I = 7 c/s), 2.07-2.86 (4H CH2, 21{ CI-I), 5.17 (4111C H = = C t t ) ; in C61-I6--0"92 (CI-I3) , 2-07-2.28 (CH2), 2.78 (CH), 5.27 (HC=); m/e 136. 3,7-Dimethylcyclo-octa-l,5-diene (2). B.p. 36°/2mm, n~°=1.4877, IRS (v, cm-1): 720, 1650 (cis-HC=CH), 1380, 1450 (C1{s). PMR (J, mln-1): in CC14--1-03 (6111CH.~, 1-----7 c/s), 2.0 (2H CH), 2.2-2.23 (4tt CH2) 5.32 (4I-I HC----); in C6116 0.97 (CHs), 2.21-2.27 (2H CH), 2.13-2.30 (4111 CH2); m/e 136. ~0 3,4-Dimethylcyclo-octa-l,5-diene (3). B.p. 40°/2mm, n/~=1,4888, IRS (v, cm-1): 720, 1650 (cis-1{C~--CH), 1380, 1450 (CH3). PMR (g, mln-~): in CCl4--0.95 (6tt CH3), 2.08--2.62 (4H CH2), 2.94 (21t CH), 5.17--5.43 (4H 11C~-); in Ce1{e 0.92 (C1{3), 1-97--2.52 (C1{2), 2.91 (Ctt), m/e 136. SUMMARY
1. A study was made of catalytic cyclodimerization of piperylene on Ni (acac)2-- P(OC6H4-- OC8H5) s- (C4H9) 3 A] at a temperature of 100°C. 2. Piperylene conversion and the selectivity of formation of end products depend on the ratio of isomeric forms of piperylene in the initial mixture. When the mixture is enriched with ci8-piperylene, 3,4- and 3,7-dimethylcyclo-l,5-octadienes with substituents in the axial positions, are formed. When the initial mixture is enriched with trans-piperylene 3,7-dimethylcyclo-
Molybdenum disulphide
105
octa-l,5-diene with substituents in the equatorial positions predominates reaction products. 3. The structure of dimethylcyclooctadiene isomers formed is confirmed by PMR and I R spectroscopy. REFERENCES
1. German Pat. 1140569, 1962; Chem. Abstrs 58, 11214, 1963 2. U.S.A. Pat. 3446862, 1969; ]:tZ hKhim. 12N, 2112, 1970 3. U. M. DZHE1KILEV, G. Ye. IVANOV and G. A. TOLSTLKOV,Neftekhimiya 15, 819, 1975
MOLYBDENUM DISULPHIDE AS HETEROGENEOUS INHIBITOR IN OXIDATION OF HYDROCARBONS* G. I. KOVAL~V, L. D. GOGITIDZE, V. I. KU~A~OVA, Yu. N. DYSHLEVSKII and Y~. T. DENISOV Institute of Chemical Physics, U.S.S.R. Academy of Sciences (Received 10 November 1975)
VARIOUS organic compounds soluble in hydrocarbons, which are homogeneous inhibitors are now used as inhibitors of oxidation of hydrocarbons. Heterogeneous inhibitors are at first sight of low activity in liquid phase in view of slow diffusion and comparatively rapid recombination of radicals. On the other hand heterogeneous inhibitors, semiconductors in particular, according to the semiconductor theory of catalysis [1], may form active centres on the surface and under given conditions m a y cause both repeated loss of chains (inhibition) and repeated formation of chains (catalysis) on an active centre. The inhibiting action of metal oxides on liquid-phase oxidation of hydrocarbons [2] has been noted in the literature. Using molybdenum disulphide we found an interesting case of repeated chain rupture on the surface of a heterogeneous inhibitor. Kinetic relations of inhibition of molybdenum disulphide also appeared to be quite different from those of homogeneous inhibitors. METHODS
Oxidation of hydrocarbons was studied in a gas,~metric static apparatus at a temperature of 125°C. A cylindrical glass reactor 30 mm in diameter and 120 cm s in volume provided with a special stirrer was used. The stirrer rotated a t a speed of 10-20 rev./sec to ensure even distribution of molybdenum di* Neftekhimiya 17, No. 3, 438-443, 1977.