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Synthesis and characterization of keto-sulphide resins
Fur. Polyra. J. Vol. 23, No. 5, pp. 389-392, 1987
0014-3057/87 $3.00+0.00
Printed in Great Britain
Pergamon Journals Lid
SYNTHESIS A N D CHARACTERIZATION OF KETO-SULPHIDE RESINS SUREra-~ R. PATEL, HASMUKH S. PATEL and SrlAr~TI R. PATEL Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar-388 120, Gujarat, India
(Received 23 July 1986; in revisedform 29 September 1986) Abstract--Polycondensations of acetophenone and its 4-chloro-, bromo-, and methyl- and 3-nitro derivatives with formaldehyde in the presence of sodium hydrosulphide afford the corresponding keto-sulphide resins. These resins have been characterized by elemental analyses, estimation of h~"n by vapour pressure osmometry, measurement of solution viscosity in DMF, i.r. spectra and thermal gravimetric analysis. The formation of the resins is explained.
INTRODUCTION The base catalyzed condensations of ketones containing ~t-hydrogen atom (such as acetone, methyl ethyl ketone, cyclo-hexanone and acetophenone) with formaldehyde are reported to afford dimeric ketones, cyclic products or ketone resins depending upon the relative proportions of the reactants [1-4]. A report has been given by D r o n o v e et al. [5] on the condensation of ketones with formaldehyde in the presence of hydrosulphide. These Russian workers [5] have reported that, if acetophenone, formaldehyde and K S H are taken in the molar ratio o f 1:2:1, poly(ketosulphide) is formed. These workers have not reported systematic characterization of these resins or evidence for the structure. Hence the present work was undertaken, dealing with the polycondensation of simple and substituted acetopbenones (see Table l) with formaldehyde in the presence of sodium hydrosulphide (NaSH). The course of the reaction leading to the formation of keto-sulphide resins is suggested. EXPERIMENTAL 4-Chloro-, bromo- and methyl- and 3-nitroacetophenones were prepared by reported methods [6, 7]. Sodium hydrosulphide was prepared by passing the required amount of dry H2S through conc. methanolic NaOH. All other chemicals were of laboratory grade. The polycondensation of all the five ketones listed in Table 1 were carried out following the details described below for the case of acetophenone. Other reaction conditions afforded mixed polycondensation but products were difficult to purify.
Condensation of acetophenone (AP) ( l mol) with aqueous formaldehyde (2.0tool) and sodium hydrosulphide (NaSH) (1 tool) in methanol To a solution of 37% aq. formaldehyde (17.8 ml, 0.2 mol) and freshly prepared NaSH (5.6 g, 0.1 mol) in methanol (100 ml), acetophenone (12.0 g, 0.1 rnol) was added in small amounts with continuous stirring. The mixture was left for 10 days at room temperature (27-30°C). It was then heated at 70°C for 6 hr. The resulting mixture was poured in 10% aq. HC1 (100 ml). The solid was filtered, washed with boiling water and allowed to dry in air. It was a white solid which softened in the range 70 to 80°C. The yield was 15 g. This resin designated as APFS resin was oxidized by excess alkaline KMnO4 at 100°C. The product was benzoic 389
acid, formed in nearly quantitative yield, the yield being calculated on the basis of structure of the repeat unit (see later). Following the above procedure, the polycondensations of other acetophenone derivatives were effected. These resins are described in Table 1.
Controlled oxidation of APFS To a solution of APFS (1.0 g) in formic acid (15 ml), 30% H202 solution (10 ml) was added. The solution was stirred for one hour at room temperature. It was then diluted with water (100rnl). The solid was filtered and washed with boiling water. It was a white solid softening in the range from 115° to 125°C. Controlled oxidations of other ketosulphide resins were carried out in the same manner. The softening points are shown in Table 1.
MEASUREMENTS
C and H contents were estimated on Colman C,H analyzer and S, C1 and Br contents by the Carius method. N content was estimated by the Dumas method. The i.r. spectra of all the keto-sulphide resins were recorded in KBr on a UR-10 spectrophotometer. The number-average molecular weights (A~n) of all resin samples were measured on a Hewlett-Packard Vapour Pressure Osmometer using DMF as solvent at 70°C and benzil as calibrant. Viscometdc measurements on solutions of the resin samples were carried out at 30° +_0. I°C using an Ubbelohde viscometer. Thermogravimetry of the keto-sulphide resins was carried out on a Linseis thermo-balance at a heating rate of 10°C min -~.
RESULTS AND DISCUSSIONS All the keto-sulphide resins are white to dull white solids softening in the range 70 to 120°C. They are formed in about 70 to 80% yield depending upon the nature of the ketone employed in the synthesis. The elemental analyses of the resins agree with the expected values. The expected values are calculated on the basis of the proposed structure of the repeat unit. -{--CH--CH 2--S---C HE--k~
&-o Ir
Ar: Phenyl, substituted (C1, Br, CH3, NO2) phenyl.
390
SUg~KI-IAR. PATELet al.,
•i~ ~i~
~.~- ~
•~
~
~
~
~,~l
s=l
,
f
- - ~ , - : ~
~.-':.,~
-
i
~;i~,~=_~,~.~. ~
•
I~
~
_~'d.=i~
.~.~
I
_ < z
o
o
391
Keto-sulphide resins The molecular weights of these resins (Table 1) are low. The resin obtained from 3-nitroacetophenone has the highest molecular weight and that obtained from 4-methylacetophenone the lowest. The trend in the molecular weight of the resins is the same as the expected trend in the reactivity of the acetophenone monomer employed for keto-sulphide resin synthesis. The difference in the reactivities of the acetophenone derivative is best reflected in the yield of the resins formed from them. As the molecular weight of these resins are low, the values of intrinsic viscosities [r/] of their solutions are low in the range 0.01 to 0.037 dl. g- 1. The trend in the i.r. spectra of these resins are explicable in terms of their proposed structures. They exhibit a carbonyl band in the region 1635-1675 cm -~, the exact position depending upon the nature of the --COAr group in the polymer chain. The position of the carbonyl band in the spectrum of the resin obtained from 3-nitroacetophenone is 1672 cm- ~which is the highest for the carbonyl bands in the spectra of the five keto-sulphide resins. All the spectra show a moderately strong band at 640 cm-x assigned to the -CH2-S-CH 2- group. It is reported that [8] the band for such a group occurs between 600 and 700 cm-1 for organic sulphides. All the keto-sulphide resins yield the corresponding benzoic acid on vigorous oxidation. This is consistent with the proposed structure of the resins. Controlled oxidation of all these keto-sulphide resins afford the corresponding keto-sulphone resins. The softening temperatures of keto-sulphide and
keto-sulphone resins are shown in Table 1. The data reveal that a keto-sulphone resin softens at a considerably higher temperature than the corresponding keto-sulphide resin. This finding agrees with the melting behaviour of organic sulphur compounds such as phenacyl sulphide and phenacyl sulphone [9, 10]. The i.r. spectra of keto-sulphone resins do not exhibit a band at 640cm -I for - S - of the --CH2-S-CH2- group but bands around 1140 cm -~ and 1340 cm -1 are attributed to asymmetric and symmetric stretching of the --CH2-SO2---CH2- group [111. Examination of the TG data of keto-sulphide resins (Table 1) and the TG curves reveals that all the resin samples undergo stepwise degradation. The first stage of slow degradation passes into a step of comparatively slower degradation. All the five samples lost more than 70% of their weight when heated to 500°C. This behaviour is unlike that of aliphatic polysulphides which are known to degrade rapidly due to cleavage of C-S-C bonds into free radicals. In the present case, the unexpectedly high stability of the resin may be due to oxidation of the - C - S - C - bond to - C - S O : C - during TGA in air and some role played by the pendant -COAr group in the repeat unit.
Course of keto-sulphide resin formation The possible steps involved in the keto-sulphide resin formation are shown in the following chart. It is consistent with the
H--S---H + CH20---*HS--CH2-'-OH I Ar---C----CH3 + HO---CH2--SH ~ Ar---C---CH2----CH2~SH
IL
~
O
(1) (2)
u
II + CH20--, Ar---C--CH2--CH2~S---CH2OH II IIl O
(3)
Ill + Ar--C---CHs----,Ar---C---CH2---CH2~S---CH2--CH2---C--Ar
II
g
O
,v
(4)
g
IV + |--, Ar---C--CH2---CH2--S---CH2--CH--CH2~SH V
(5)
~--Ar
(cf. 2)
II O V + CH20---, Ar--C--CH2--CH2--S---CH2---CH---CH2--S---CH2OH Vl
(6)
~--Ar
(cf. 3)
o// VI + A r - - C - - - C H 3 - - , A r - - C - - - C H - - C H 2 ~ S - - C H 2 - - - C H - - C H 2 - - S - - C H 2 - - C H 2 - - C - - A r O ][
[~
VII
~--Ar
IL
O VII
(i) CH20 ,
(ii) Ar--C---CH 3
II
0
keto-sulphide resin.
O[I
(7) (cf. 4)
392
SUREKHAR. PATELet al.
molar reaction of the ketone, formaldehyde and sodium hydrosulphide (1:2:1) required for the synthesis. The first step involved in the formation of a mercapto-methanol (I) is well established [12, 13]. The reactivity of I in step 2 is also very well known [5]. The type of reaction involved in step 1 is repeated in steps 3,5 etc. The type of reaction involved in step 2 is repeated in steps 4,7 etc. The proposed mechanism will also explain the formation of diketosulphide when ketone is used in excess. Further work in connection with the curing of keto-sulphide resins and their application for composite materials is under progress. Acknowledgements--The authors thank Professor R. P. Patel, Head, Department of Chemistry, S. P. University, Vallabh Vidyanagar-388120 for providing necessary facilities. REFERENCES
I. M. T. Harvey and P. L. Rosamilla. U.S. Patent 2,828,820 Apr. 1 (1958) C.A. 52, 15889f.
2. Abo Masahiro C. Kogyo Kagaki Zasshi 71, 1266, 1271 (1968). 3. Abo Masahiro C. Kogyo Kagaki Zasshi 72, 1366, 1371, 1372 (1969). 4. M. M. Tilichenko and R. M. Buzunova. Zhur. Prikl. Khim., Mosk 27, 77 (1954). 5. V. I. Dronov, R. F. Nigmatullina, L. M. Khalilov and Yu. E. Nikitin. Zh. Org. Khim. 16, 1392 (1980). 6. B. B. Corson and R. K. Hazen. Org. Syn. Coll. II, 434 (1947). 7. Vogel's Textbook of Practical Organic Chemistry. 4th Edn. E4BS/Longman, London (1978). 8. J. R. Trotter and H. W. Thomson. J. Chem. Soc. 481 (1946). 9. W. Tafel and B. Mauritz. Bet. dr. chem. Ges. 23, 3474 (1890). 10. E. Fromm and B. Flaschen. Justus Liebigs Annln Chem. 394, 312 (1890). ll. K. C. Schreiber. Analyt. Chem. 21, 1108 (1949). 12. E. Baumann. Bet. 23, 60 (1890). 13. A. Hasemann. Ann. 126, 293 (1863).
0014-3057/87 $3.00+0.00
Printed in Great Britain
Pergamon Journals Lid
SYNTHESIS A N D CHARACTERIZATION OF KETO-SULPHIDE RESINS SUREra-~ R. PATEL, HASMUKH S. PATEL and SrlAr~TI R. PATEL Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar-388 120, Gujarat, India
(Received 23 July 1986; in revisedform 29 September 1986) Abstract--Polycondensations of acetophenone and its 4-chloro-, bromo-, and methyl- and 3-nitro derivatives with formaldehyde in the presence of sodium hydrosulphide afford the corresponding keto-sulphide resins. These resins have been characterized by elemental analyses, estimation of h~"n by vapour pressure osmometry, measurement of solution viscosity in DMF, i.r. spectra and thermal gravimetric analysis. The formation of the resins is explained.
INTRODUCTION The base catalyzed condensations of ketones containing ~t-hydrogen atom (such as acetone, methyl ethyl ketone, cyclo-hexanone and acetophenone) with formaldehyde are reported to afford dimeric ketones, cyclic products or ketone resins depending upon the relative proportions of the reactants [1-4]. A report has been given by D r o n o v e et al. [5] on the condensation of ketones with formaldehyde in the presence of hydrosulphide. These Russian workers [5] have reported that, if acetophenone, formaldehyde and K S H are taken in the molar ratio o f 1:2:1, poly(ketosulphide) is formed. These workers have not reported systematic characterization of these resins or evidence for the structure. Hence the present work was undertaken, dealing with the polycondensation of simple and substituted acetopbenones (see Table l) with formaldehyde in the presence of sodium hydrosulphide (NaSH). The course of the reaction leading to the formation of keto-sulphide resins is suggested. EXPERIMENTAL 4-Chloro-, bromo- and methyl- and 3-nitroacetophenones were prepared by reported methods [6, 7]. Sodium hydrosulphide was prepared by passing the required amount of dry H2S through conc. methanolic NaOH. All other chemicals were of laboratory grade. The polycondensation of all the five ketones listed in Table 1 were carried out following the details described below for the case of acetophenone. Other reaction conditions afforded mixed polycondensation but products were difficult to purify.
Condensation of acetophenone (AP) ( l mol) with aqueous formaldehyde (2.0tool) and sodium hydrosulphide (NaSH) (1 tool) in methanol To a solution of 37% aq. formaldehyde (17.8 ml, 0.2 mol) and freshly prepared NaSH (5.6 g, 0.1 mol) in methanol (100 ml), acetophenone (12.0 g, 0.1 rnol) was added in small amounts with continuous stirring. The mixture was left for 10 days at room temperature (27-30°C). It was then heated at 70°C for 6 hr. The resulting mixture was poured in 10% aq. HC1 (100 ml). The solid was filtered, washed with boiling water and allowed to dry in air. It was a white solid which softened in the range 70 to 80°C. The yield was 15 g. This resin designated as APFS resin was oxidized by excess alkaline KMnO4 at 100°C. The product was benzoic 389
acid, formed in nearly quantitative yield, the yield being calculated on the basis of structure of the repeat unit (see later). Following the above procedure, the polycondensations of other acetophenone derivatives were effected. These resins are described in Table 1.
Controlled oxidation of APFS To a solution of APFS (1.0 g) in formic acid (15 ml), 30% H202 solution (10 ml) was added. The solution was stirred for one hour at room temperature. It was then diluted with water (100rnl). The solid was filtered and washed with boiling water. It was a white solid softening in the range from 115° to 125°C. Controlled oxidations of other ketosulphide resins were carried out in the same manner. The softening points are shown in Table 1.
MEASUREMENTS
C and H contents were estimated on Colman C,H analyzer and S, C1 and Br contents by the Carius method. N content was estimated by the Dumas method. The i.r. spectra of all the keto-sulphide resins were recorded in KBr on a UR-10 spectrophotometer. The number-average molecular weights (A~n) of all resin samples were measured on a Hewlett-Packard Vapour Pressure Osmometer using DMF as solvent at 70°C and benzil as calibrant. Viscometdc measurements on solutions of the resin samples were carried out at 30° +_0. I°C using an Ubbelohde viscometer. Thermogravimetry of the keto-sulphide resins was carried out on a Linseis thermo-balance at a heating rate of 10°C min -~.
RESULTS AND DISCUSSIONS All the keto-sulphide resins are white to dull white solids softening in the range 70 to 120°C. They are formed in about 70 to 80% yield depending upon the nature of the ketone employed in the synthesis. The elemental analyses of the resins agree with the expected values. The expected values are calculated on the basis of the proposed structure of the repeat unit. -{--CH--CH 2--S---C HE--k~
&-o Ir
Ar: Phenyl, substituted (C1, Br, CH3, NO2) phenyl.
390
SUg~KI-IAR. PATELet al.,
•i~ ~i~
~.~- ~
•~
~
~
~
~,~l
s=l
,
f
- - ~ , - : ~
~.-':.,~
-
i
~;i~,~=_~,~.~. ~
•
I~
~
_~'d.=i~
.~.~
I
_ < z
o
o
391
Keto-sulphide resins The molecular weights of these resins (Table 1) are low. The resin obtained from 3-nitroacetophenone has the highest molecular weight and that obtained from 4-methylacetophenone the lowest. The trend in the molecular weight of the resins is the same as the expected trend in the reactivity of the acetophenone monomer employed for keto-sulphide resin synthesis. The difference in the reactivities of the acetophenone derivative is best reflected in the yield of the resins formed from them. As the molecular weight of these resins are low, the values of intrinsic viscosities [r/] of their solutions are low in the range 0.01 to 0.037 dl. g- 1. The trend in the i.r. spectra of these resins are explicable in terms of their proposed structures. They exhibit a carbonyl band in the region 1635-1675 cm -~, the exact position depending upon the nature of the --COAr group in the polymer chain. The position of the carbonyl band in the spectrum of the resin obtained from 3-nitroacetophenone is 1672 cm- ~which is the highest for the carbonyl bands in the spectra of the five keto-sulphide resins. All the spectra show a moderately strong band at 640 cm-x assigned to the -CH2-S-CH 2- group. It is reported that [8] the band for such a group occurs between 600 and 700 cm-1 for organic sulphides. All the keto-sulphide resins yield the corresponding benzoic acid on vigorous oxidation. This is consistent with the proposed structure of the resins. Controlled oxidation of all these keto-sulphide resins afford the corresponding keto-sulphone resins. The softening temperatures of keto-sulphide and
keto-sulphone resins are shown in Table 1. The data reveal that a keto-sulphone resin softens at a considerably higher temperature than the corresponding keto-sulphide resin. This finding agrees with the melting behaviour of organic sulphur compounds such as phenacyl sulphide and phenacyl sulphone [9, 10]. The i.r. spectra of keto-sulphone resins do not exhibit a band at 640cm -I for - S - of the --CH2-S-CH2- group but bands around 1140 cm -~ and 1340 cm -1 are attributed to asymmetric and symmetric stretching of the --CH2-SO2---CH2- group [111. Examination of the TG data of keto-sulphide resins (Table 1) and the TG curves reveals that all the resin samples undergo stepwise degradation. The first stage of slow degradation passes into a step of comparatively slower degradation. All the five samples lost more than 70% of their weight when heated to 500°C. This behaviour is unlike that of aliphatic polysulphides which are known to degrade rapidly due to cleavage of C-S-C bonds into free radicals. In the present case, the unexpectedly high stability of the resin may be due to oxidation of the - C - S - C - bond to - C - S O : C - during TGA in air and some role played by the pendant -COAr group in the repeat unit.
Course of keto-sulphide resin formation The possible steps involved in the keto-sulphide resin formation are shown in the following chart. It is consistent with the
H--S---H + CH20---*HS--CH2-'-OH I Ar---C----CH3 + HO---CH2--SH ~ Ar---C---CH2----CH2~SH
IL
~
O
(1) (2)
u
II + CH20--, Ar---C--CH2--CH2~S---CH2OH II IIl O
(3)
Ill + Ar--C---CHs----,Ar---C---CH2---CH2~S---CH2--CH2---C--Ar
II
g
O
,v
(4)
g
IV + |--, Ar---C--CH2---CH2--S---CH2--CH--CH2~SH V
(5)
~--Ar
(cf. 2)
II O V + CH20---, Ar--C--CH2--CH2--S---CH2---CH---CH2--S---CH2OH Vl
(6)
~--Ar
(cf. 3)
o// VI + A r - - C - - - C H 3 - - , A r - - C - - - C H - - C H 2 ~ S - - C H 2 - - - C H - - C H 2 - - S - - C H 2 - - C H 2 - - C - - A r O ][
[~
VII
~--Ar
IL
O VII
(i) CH20 ,
(ii) Ar--C---CH 3
II
0
keto-sulphide resin.
O[I
(7) (cf. 4)
392
SUREKHAR. PATELet al.
molar reaction of the ketone, formaldehyde and sodium hydrosulphide (1:2:1) required for the synthesis. The first step involved in the formation of a mercapto-methanol (I) is well established [12, 13]. The reactivity of I in step 2 is also very well known [5]. The type of reaction involved in step 1 is repeated in steps 3,5 etc. The type of reaction involved in step 2 is repeated in steps 4,7 etc. The proposed mechanism will also explain the formation of diketosulphide when ketone is used in excess. Further work in connection with the curing of keto-sulphide resins and their application for composite materials is under progress. Acknowledgements--The authors thank Professor R. P. Patel, Head, Department of Chemistry, S. P. University, Vallabh Vidyanagar-388120 for providing necessary facilities. REFERENCES
I. M. T. Harvey and P. L. Rosamilla. U.S. Patent 2,828,820 Apr. 1 (1958) C.A. 52, 15889f.
2. Abo Masahiro C. Kogyo Kagaki Zasshi 71, 1266, 1271 (1968). 3. Abo Masahiro C. Kogyo Kagaki Zasshi 72, 1366, 1371, 1372 (1969). 4. M. M. Tilichenko and R. M. Buzunova. Zhur. Prikl. Khim., Mosk 27, 77 (1954). 5. V. I. Dronov, R. F. Nigmatullina, L. M. Khalilov and Yu. E. Nikitin. Zh. Org. Khim. 16, 1392 (1980). 6. B. B. Corson and R. K. Hazen. Org. Syn. Coll. II, 434 (1947). 7. Vogel's Textbook of Practical Organic Chemistry. 4th Edn. E4BS/Longman, London (1978). 8. J. R. Trotter and H. W. Thomson. J. Chem. Soc. 481 (1946). 9. W. Tafel and B. Mauritz. Bet. dr. chem. Ges. 23, 3474 (1890). 10. E. Fromm and B. Flaschen. Justus Liebigs Annln Chem. 394, 312 (1890). ll. K. C. Schreiber. Analyt. Chem. 21, 1108 (1949). 12. E. Baumann. Bet. 23, 60 (1890). 13. A. Hasemann. Ann. 126, 293 (1863).