ORGANOSULFUR COMPOUNDS FROM LONG-CHAIN EPOXIDES E R I C H
T O B L E R
Research and Decelopment Department, Chemicals and Plastics, Union Carbide Corp., South Charleston, W . V u . 25303 1,2-EpithioaIkanes, 2-hydroxyalkanethiols, 1 ,2-alkanedithiols, bis( 2-hydroxyalkyl) sullfides (including their sulfoxides and sulfones), 1 -dimethylamino-2-alkanethiolsf arid 1 -methylamino-2-alkanethiols were prepared from long-chain ( C&I,) 1,2epoxyalkanes. The reaction between episulfides and dimethylamine, methylamine, arid ammonia resulted in the formation of different products depending on the choice of solvent.
HIGH yields of 1,2-epit,hioalkanes (I) have been prepared from the corresponding 1,2-epoxyalkanes and thiourea. The compounds are less prone to spontaneous polymerization than the simpler aliphatic episulfides and are stable up to about 120" C. Treatment of the epoxides and episulfides (I) with potassium hydrogen sulfide yielded 2-hydroxyalkanethiols (11) and 1,2-alkanedithiols (III), respectively. T h e basecatalyzed reaction between epoxides and I1 afforded bis(2hydroxyalkyl) sulfides (IV), which were oxidized to their corresponding sulfoxides (V) and sulfones (VI). The reaction between the episulfides (I) and dimethylamine resulted in the formation of l-dimethylamino2-alkanethiols (VII). With methylamine, the corresponding l-methylamino2-alkanethiols (VIII) were formed only in the presence of nonpolar solvents. I n polar solvents, the formation of VI11 was suppressed in favor of episulfide polymerization. In the case of ammonia, no conditions could be found that would lead to this formation of aminoalkanethiols. The employment of polar solvents resulted in the formation of polyepisulfides, and in the presence of nonpolar solvents, desulfurization t o a-olefins occurred. Most of the compounds exhibit biological activity. A reaction scheme for the compound classes prepared is given in Figure 1. RCL.I-CH2 l l OH S H
IV
II
I
RCH -CHI \
13
/
RCF?H2
R C H - C H 2 - S - C H 2 - CHR I
I
OH
OH
E MeC03H
RCH -
H p - S - CH2-C H . R
l
I
OH SH
m
YHMe
RCli I
si
- C1 H 2
1
OH
9
SH
XS
;II
MeCC,H
0 I1
RCH-CHZ-S-CHZ-CHR I
ll
OH
0
I
OH
PI Figure 1. Reaction scheme for production of organosulfur compounds from long-chain epoxides
T h e reaction of epoxides with numerous nucleophiles has been investigated extensively from both a mechanistic and a synthetic standpoint. However, a study of the literature reveals that almost all of the reactions described are restricted to relatively short-chain epoxides. The increasing importance of a-olefins as raw materials in chemical industry prompted an investigation of some of their derivatives. This paper describes the syntheses of long-chain sulfur compounds that can be obtained from the now readily available long-chain 1,2-epoxyalkanes. 1,2-EpithioaIkanes
When comparing episulfides with their oxygen analogs it can be stated that the episulfides are more prone to spontaneous polymerization than the corresponding epoxides and that the desulfurization of episulfides takes place much more readily than the similar deoxygenation of epoxides. The simplest episulfide, ethylene sulfide, was first reported in 1920 (Delepine, 1920a,b; Staudinger and Siegwart, 1920). A comprehensive review of the field appeared in 1955 (Schoenberg, 1955), and more recent aspects of olefin sulfide chemistry are discussed by Goodman and Reist (1966). The most convenient general method for the preparation of episulfides is the direct conversion of the corresponding epoxide with thiocyanate ion or thiourea. For certain reactions thiourea is the preferred reagent and for others thiocyanate gives better results; a survey of the literature shows that no generalization as to the choice of reagent is possible. A mechanism for the thiocyanate reaction was first advanced by Ettlinger (1950) and given support by van Tamelen (1951). Culvenor et al. (1952) proposed a similar mechanism for the thiourea reaction. The only long-chain 1,2-episulfide described in the literature is 1,2-epithiooctane (Moore and Porter, 1958),which was prepared from 1,2-epoxyoctane and thiourea in the presence of acid to minimize alkali-catalyzed polymerization of the product (Bordwell and Andersen, 1953). During the preparation of long-chain episulfides by the thiourea route polymerization was found to be negligible and therefore the presence of acid is not necessary for obtaining high product yields. The procedure consists simply in treating equimolar amounts of epoxides and thiourea in alcohol. The reaction is exothermic and without external heat requires about 16 to 22 hours for a 9 5 7 conversion. In refluxing methanol, the reaction is usually complete in 2 to 4 hours. A t the VOL. 8 NO. 4 DECEMBER 1969
415
Table 1. Yields and Physical Data of 1,2-EpithioaIkanes (I) i;
Yield
R
Crude
Dist.
C6 C8 C 14, Ci,
95.8 97.5 96.0 85.4
77 75 82
. ..
B.P., C. IMm.)
Table 111. Yields and Physical Data of 1,2-AIkanedithiols (111)
82-83" (10)" 61-62" (0.4) 90-91" (0.5) Decomp. (0.5)
R
1.4708 (25)' 1.4712 (25.5) 1.4702 (25.5)
Ce Cr CIN
...
C,?
Moore and Porter (1958) report b.p. 83" at 5 mm., and ng 1.4702.
end of the reaction, water is added to dissolve the crystallized urea and the episulfide is extracted with ether. Vacuum distillation affords the episulfides (I, R=Cs, CR, and (2,") as water-clear liquids of high purities. The C14episulfide (I, R = C U ) underwent thermal desulfurization during distillation, yielding a distillate which contained 82% I-tetradecene. Yields and physical data of the episulfides prepared are summarized in Table I.
Crude
Distd.
CG
82.4" 78.6b 89.3' 89.0
75 63 77 76
c 1 2
'75 72 73 67
69-70 92-93 115-16 142-43
(0.3) (0.3) (0.3) (0.15)
~
1.5005 1.4953 1.4915 1.4882
C. (25.5) 125.5) (p5.5) (20)
99+ 99t 99+ 36
Swern, Billen, and
Culvenor, Davies, and Heath (1949) found that attack of hydrogen sulfide anion on episulfides produces vicinal dithiols together with polymeric material. We found, in contradistinction to Moore and Porter (19581, t,hat in the case of long-chain dithiols, polymerization is practically nil. The low yield of 1,2-octanedithiol (-3%) obtained by these authors might be due to excessive contact times (3 days) and/or different work-up procedure. In our hands, the dithiols were obtained in high yields a t contact times of 4 to 5 hours. Yields and physical data of the 1,2-alkanedithiols prepared are given in Table 111. Bis( 2-hydroxyalkyl) Sulfides (IV)
Bis(2-hydroxyalkyl) sulfides can be prepared either by the base-catalyzed addition of hydrogen sulfide to longchain epoxides a t higher temperatures (Umbach et al., 1969) or by the interaction of 2-hydroxyalkanethiols with 1,2-epoxyalkanes. I n general, the ring opening of epoxides with mercaptans is carried out in the presence of alkalies or the corresponding alkali mercaptides a t elevated temperatures. Kaufmann and Schickel (1963) found that the strongly basic ion exchanger Amberlite IRA 400 in the OH form is an excellent catalyst for this reaction. We have successfully utilized this resin to catalyze the reaction between 1,2-epoxyalkanes and 2-hydroxyalkanethiols. The reaction between 1,2-epoxyalkanes and 2-hydroxyalkanethiols was carried out in refluxing isopropyl ether and in the presence of a catalytic amount of Amberlite IRA 400 in the OH form. The progress of the reaction was followed by periodic sampling and VPC analysis of the samples. After completion of the reaction (usually 16 to 18 hours), the reaction mixture was filtered in the heat to remove the catalyst, and the product was precipitated by cooling the filtrate. I n Table IV are summarized yields and physical properties of the bis(2-hydroxyalkyl) sulfides prepared.
B.P., C. (mm.) 60-61 85-86 103-04 123-25
nD
(0.3) (0.35) (0.4) (0.4)
Table II. Yields and Physical Data of 2-Hydroxyalkanethiols (11) Our Data
R
c1,
97 96 95.3 92
Purity ( VPLj
1,2-AIkanedithiols (111)
The opening of an epoxide ring by a nucleophile is closely analogous to ordinary bimolecular nucleophilic substitution, and the attack occurs preferentially a t the less substituted carbon (Gould, 1959). Therefore, the reaction of 1,2-epoxyalkanes with hydrogen sulfide anion should result in the formation of 2-hydroxyalkanethiols (11). At the time our investigations were in progress, longchain 2-hydroxyalkanethiols were not described in the literature. After completion of our work, Umbach, Mehren, and Stein (1969) published a comprehensive study on the synthesis of long-chain hydroxyalkylmercaptans by the base-catalyzed reaction of hydrogen sulfide with longchain epoxides. I n the course of their investigation they prepared the C8, CI2, and CI8 hydroxyalkanethiols and presented proof (KMR) that the compounds are indeed 2-hydroxyalkanethiols (11). I n the present work, 2-hydroxyalkanethiols were prepared by the addition of the epoxides to an ice-cold solution of potassium hydrogen sulfide in methanol, prepared according to the directions of Culvenor et al. (1949). The reaction is usually complete in 1 to 2 hours (as determined by vapor-phase chromatography) and affords 2-hydroxyalkanethiols in 80 to 90% yields. Dimeric by-productsbis(2-hydroxyalkyl) sulfides-which are formed in a second reaction step between the primary product and still available epoxyalkane, are present only in minor amounts. Yields of the 2-hydroxyalkanethiols prepared are summarized in Table 11, and their physical data are compared to those in the literature (Umbach et al., 1969). Although the literature values differ widely from our own, our data are in line with corresponding 1,2-dithiols (see Table 111)
C8
Crude Distd. B.P., ' C. (Mm.)
and the corresponding 1,2-diols-e.g., Scanlan (1946).
2-Hydroxyalkanethiols ( II)
% Yield
r' r
7 ; Yield
n D , C.
nD,
O C .
1.4740 (25.5) 1.4745 (25.5) 1.4740 (25.5)
...
M.p., " C.
... ...
...
38-39
Literature Data O
B.P., C. (mm.) 76 (0.05)
112-;3 (0.01)
...
-
M . p . , C:.
... ... 26.7
...
And 14.6% bk(2-hydroxyoctyl) sulfide, m.p. 45-49". *and 17.9% bis(2-hydroxydecyl) sulfide, m.p. 57-63", 'and his(2-hydrorydodecyl) sulfide, m.p. 54 Go,isolabd from distillation residue. ~~
~~
416
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
Table V. Yields and Physical Data of Bis(2-hydroxyalkyl) Sulfoxides ( V )
Table IV. Yielcrs and Physical Properties of Bis(2-hydroxyalkyl) Sulfides ( I V ) lIZPcn,std .)
Krcrystg. Solwnt
Melting Range, ' C
56 70 76 78
Pentane-hexane HPxane Hexane Methanol
45-51 59--65 64-73" 65-72
1
K
c c:,, /,
,'i
c:i,
"
i'ield
Yield of Rectytd IEtOAc) Product
K
Melting Range, O C
100-25
63 81 70 77
103-25 93 -103 100-04
L;?lbach. Mehren, and Stein (1969) report r i p 82-83'.
Table VI. Bis(2-hydroxyalkyl)Sulfones ( V I )
Bis( 2-hydroxyalkyl) Suilfoxides ( V ) and Bis( 2-hydroxyalkyl) Suilfones ( V I )
A large variety of methods for the oxidation of sulfides to sulfoxides and sulfoiies have been reported. The most commonly used oxidizing agent appears to be 30' i hydrogen peroxide in glacial acetic acid. l h e sulfoxide is formed readily, but the sulfone reaction is slower, generally requiring heat. For the oxidation of hydroxyl groups containing sulfides to the corresponding sulfones, Schulz et oi. (1963) recommended the use of tungsten, molybdengJm, or vanadium catalysts with hydrogen peroxide in wafer. These authors claim that this method eliminates secondary degradative oxidation reactions, gives good yields, simplifies product isolation and purification, and conserves reagent. A n oxidation run, carried out in the / HLOaccording to the recommended presence of H r O L WO procedure, gave a mixture of sulfoxide and sulfone. Later experiments have shown that the conversion of hydroxysulfides to the corresponding sulfoxides as well as the sulfones proceeds very smoothly with peracetic acid as the oxidizing agent. The bis(2-hydroxyalkyl) sulfides ( I V ) were readily oxidized to the sulfoxicles with equimolar amounts of peracetic acid in the cold. Yields and physical properties of the sulfoxides (VI prepared are given in Table V. The sulfones ( V I ) were obtained either directly from the sulfides ( I V ) or from the sulfoxides (V) in the presence of excess peracetic acid a t room temperature. Pertinent data of the sulfones ( V I ) prepared are tabulated in Table G
V1. Reaction of 1,2-Epithioalkanes w i t h Amines
'The attempted preparation of aminothiols by the reaction of ethylene sulfide with aqueous or alcoholic ammonia resulted only in the formation of solid polymers containing a very low percentage of nitrogen (Delepine, 1920a,b; Delepine and Eschenbrenner, 1923). The same results were reported a few years later by Reppe and Kicolai (1936). Snyder et al. (1947), ;starting from ethylene, propylene, isobutylene, and cyclolhexene sulfides, prepared a variety of aminothiols and, 011 the basis of a color test, believed the products (from isobutylene sulfide and secondary amines) to be tertiary mercaptans. Braz (1951) found that ethylene sulfide is polymerized completely in the presence of a solution of an amine that is a strong base in an ionizing solvent, thus evading a reaction with the amine. T o suppress polymerization, he recommended the use of nonpolar solvents as rcsction media. Although conditions for the preparation of aminothiols by the reaction of' epiisulfides with secondary amines are new well established, the ring opening of substituted 1,2episulfides is still open. to discussion. Keppe and Nicolai (1936) apparently obtained a primary mercaptan by
R C,
c, CI,, c>2
Startirg Material
Moles Peracetic Mole Startg. Mat.
Me1t iqq Range, ' C
Sulfoxide Sulfoxide Sulfoxide Sulfide
2 2 2 3
119-21 120-25 116-21 112-20
treating propylene sulfide with n-butylamine, whereas Snyder et al. (1947) believed that in their work (from propylene sulfide and di-n-amylamine) the product was a secondary thiol, Hansen (1959) presented indirect proof that the opening of the propylene sulfide ring by dimethylamine leads to a primary mercaptan and suggested a cyclic sulfonium ion as an intermediate. Based on kinetic studies, Oddon and Wylde (1967) concluded that the ring opening reaction of episulfides by an amine is a SNl attack of the amine a t the less substituted carbon. Dimethylamine. The reaction between long-chain episulfides and dimethylamine proceeds smoothly under a variety of reaction conditions to give dimethylaminothiols in high yields. Even in the presence of highly polar solvents such as ethanol (conditions under which ethylene sulfide is completely polymerized), polymerization of the episulfide is negligible. Conditions, yields, and physical properties of the 1-dimethylamino-2-alkanethiolsprepared are summarized in Table VII. Proof that the products are secondary thiols was obtained from an examination of the N M R spectrum of the 1-dimethylamino-2-octanethiol(A). The spectrum exhibits a broad signal (1 proton) a t 62.8, a sharp singlet superimposed on a multiplet (9 protons) a t 62.2, an unresolved mutliplet (10 protons) a t 61.3, and a triplet (3 protons) a t 60.90. The 60.90 and 61.3 signals represent the methyl (a)and methylene ( b ) of the alkyl group. The signals a t 62.2 represent protons d and e plus one other proton. This proton was shown to be the SH proton ( f ) by treatment of the sample with DLO,which results in an intensity loss in this signal. The broad signal a t 62.8 therefore must be the methine proton (c) deshielded by S, and since it has a count of one proton, the structure must be A. The corresponding signal in B would have a count of 2 protons.
a
B
Methylamine. Methylamine also reacts smoothly with long-chain episulfides; however, the desired methylaminoalkanethiols are formed only in nonpolar solvents. VOL. 8 NO. 4 DECEMBER 1 9 6 9
417
Table VII. Reaction Conditions, Yields, and Physical Properties of 1 -Dirnethylamino-2-alkanethiols
B.P., C. (Mm.)
Yield (Crude)
((
R
Reaction Condition.?
Ci C. C, CI,, C!?
C!?
4 hr.: 100" in C6H6 5 days at R.T. in Et20 4 hr.! 100' in C,Hh 4 hr. I looc in CGHL 3 hr.;76O in EtOH 4 hr. 100" in C,H, I
91 21 93 92 65
M HC1-Salt . P . , C. nD
1.4640
53-54 (0.2)
76 (0.2) 110 (0.3)
78
181-82Q
1.4645
188-88.5"
1.4648
181-82"
...
-145 (0.4)9
182-83.5"
' Recpstaliized from mixfure of ethyl acetate and 2-propanoi. " Product partially decomposed to olefin upon i'acuum distiilation.
Table VIII. Reaction Condition, Yields, and Product Description of 1 -Methylamino-2-alkanethiols (VIII) (c
K C
f1
Ch
C, C. C,,, CL
Reaction Conditiom 2.5 hr. 169' in EtOH"' 4 hi-; 100" in C,& 1.5 hr.:63s in EtOH 2 hr. :100" + 2 hr. 150" in Cr;H,; 2 hr.;100" + 2 hr.. 150' in C,;H, 4 hr./ 150' in C,,Hti
Yield
(Crude)
Product
100 71 100 90 90
Polyepisulfide VI11
Polyepisulfide VI11 VI11 VI11
78
n440'1 aqueous MeiVH, used for this reaction. I n all other runs, anhydrous Me"? f m m pentane.
In polar solvents such as ethanol, the reaction with methylamine is suppressed in favor of episulfide polymerization. Reaction conditions, yields, and product descriptions are given in Table VIII. Unfortunately, the K M R spectrum of the methylaminoalkanethiols did not allow a clear-cut structure assignment as was the case for the corresponding dimethylaminoalkanethiols. By analogy, however, it is reasonable t o assume that the products are of the A type-that is, 1-methylamino-2-alkanethiols. Ammonia. We have not been able to obtain unsubstituted aminoalkanethiols RCH(SH)CH2NH? by the reaction of long-chain episulfides with ammonia. Here again, polyepisulfides are formed in the presence of highly polar solvents. I n nonpolar solvents unchanged episulfide can be recovered a t low reaction temperatures, whereas a t elevated temperatures decomposition to a-olefins occurs. In solvents of medium polarity, polymerization and desulfurization reactions take place simultaneously. The various conditions, under which ammonia has been treated with epithioalkanes, are summarized in Table IX.
418
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
37-40b Viscous oil 48-49 55-56' 60-61'
uas employed. B.p. 56-57" at 0.2 mm. LRecrystallized
Experimental
1,2-Epoxyalkanes. Commercial @-olefins were treated with peracetic acid and the epoxides thus formed purified by distillation. 1,2-Epithiodecane. To a stirred mixture of 22.8 grams of thiourea (0.3 mole) and 100 ml. of methanol was added within 15 to 20 minutes 46.8 grams of 1,2-epoxydecane (0.3 mole). The temperature rose to 40" and after it started to fall again, the reaction mixture was refluxed for 3 hours. After cooling, water was added to dissolve the crystallized urea, and the product was extracted with ether. After drying, the ether was removed, and the residual oil was vacuum distilled to give 39.2 grams (76%) of 1,2-epithiodecane (b.p. 61-62" a t 0.4 mm., ng 1.4712). Anal. Calcd. for CloH20S: C, 69.70; H , 11.70; S, 18.61. Found: C, 70.02; H, 11.60; S, 18.46. 2-Hydroxyoctanethiol. An ice-cooled solution of 11.2 grams of potassium hydroxide (0.2 mole) in 100 ml. of methanol was saturated with hydrogen sulfide. After the saturation point had been reached (as indicated by blackening of lead acetate paper on top of condenser), the H2S flow was reduced, and 25.6 grams of 1,2epoxyoctane (0.2 mole) was added within 5 minutes. After one hour, VPC analysis indicated the presence of 2.3%
Biological Properties and Possible Uses
Most of the compounds described exhibit biological activity. Bactericidal activity is shown by some of the members of class I, 111, IV, V, and VI compounds; fungicidal properties are displayed by compound classes I, 11, 111, VI, and VIII. Whereas the episulfides (I) show pre-emergent herbicidal activity, postemergence herbicidal properties are shown by the 11, 111, VII, and VI11 type compounds. I n addition, I , 11, 111, IV, and V possess also a low degree of insecticidal activity. Some of the compounds appear t o be useful in analytical chemistry or as crosslinking agents in the vulcanization of rubber. The aminoalkanethiols and salts thereof are cationic type surfactants which might have pptential as components in shampoos and other cosmetic preparations used for the treatment of hair.
M . P . , C. Viscous oil
~~
Table IX. Reaction of 1,5-Epithioalkanes with Ammonia R
Reaction Conditions
Remarks or Product(s)
47 hr./16-32' in EtOH 20-24 h r . / l 5 P in (i-Pr)?O C, 6 hr.;46-56" in E t O H Cx 5.5hr./25-2? in CsH6 CR 4 hr./86-100' in hexane C , 5.5 hr./144-50" in hexane C l 0 2.5 hr./14-7O0 in (i-Pr)20 C1,, 4 hr./100" in (i-Pr)LO
Polyepisulfide', viscous oil 1-Octene and oligomers Polyepisulfide, viscous oil KO reaction No reaction 45% 1-decene + 557~episulfide KO reaction 25% solid prod. + 7 0 5 episulfide CI,, 7 hr./ 150" in MeO(CH2)rOMe Olefin, oligomers, polymers.
Cs Ch
0
3' 'j ; c aqueous NH1 used for this reaction. I n all other r u m , (1
anhydrous N H , was employed.
1,2-epoxyoctane, 82.4% 2-hydroxyoctanethiol, and 14.6% bis(2-hydroxyoctyl) sulfide. After standing overnight, 100 ml. of water and 100 1711. of 2 N sulfuric acid were added, and the mixture was extracted with ethyl acetate. The extract was washed with water, saturated sodium bicarbonate solution, again with water, and dried. After evaporation of the solvent, the residue was vacuum-distilled to give 24.3 grams (75%) of 2-hydroxyoctanethiol (b.p. 60-61" a t 0.3 mm., a:'' 1.4740). Anal. Calcd. for C8HlsOS: C, 59.20; H , 11.18; S, 19.76. Found: C, 59.80; H , 11.07; S,19.11. Short-way vacuum distillation of the residue (4.0 grams) afforded 2.6 grams (971) of bis(2-hydroxyoctyl) sulfide (m.p. 45-49"). Anal. Calcd. for CIGIId40?S: C, 66.15; H , 11.80; S,11.04; C, 65.79; H , 11.71; S, 11.30. 1,2-Dodecanedithiol. An ice-cold solution of 5.6 grams of potassium hydroxide (0.1 mole) in 50 ml. of methanol was saturated with hydrogen sulfide, the H,S flow reduced, and 20.0 grams of 1,2!-epithiododecane (0.1 mole) added within 7 minutes. After completion of the addition, the reaction mixture was allowed to warm up to room temperature. After 4 hours a t room tempeyature, VPC analysis indicated the presence of 95.3% 1,2-dodecanedithiol. Water and 2N sulfuric acid were added, and the mixture was extracted with ethyl acetate. The extract was washed several times with water and dried, the solvent evaporated, and the residue distilled in vacuo to give 17.1 grams (73%) of 1,2-dodecanedithiol (b.p. 115-16" a t 0.4 mm., ngd 1.4915). Anal. Calcd. for C1."&: C, 61.46; H , 11.18; S, 27.35. Found: C , 61.87; H , 11.22; S, 26.76. Bis(2-hydroxydecyl) Sulfide. A mixture of 9.5 grams of 2-hydroxydecanethiol (0.05 mole), 7.8 grams of 1,2epoxydecane (0.05 mole), 50 ml. of isopropyl ether, and 2.5 grams of Amberlite IRA 400 ion exchange resin in the OH form was refl.uxed under a nitrogen blanket for 18 hours. The reaction mixture was filtered hot and the clear filtrate was cooled to give 13.3 grams (70%) of pure IV ( R = C,) (m.p. 59-65"). Anal. Calcd. for Cr,,H4202S: C, 69.32; H , 12.22; S, 9.23. Found: C, 69.54; H , 12.27; S, 8.96. Bis(2-hydroxydecyl) Sulfoxide. A slurry of 6.9 grams of bis(2-hydroxydecyl) sulfide (0.02 mole) in 75 ml. of ethyl acetate was cooled to O", and 8.0 grams of 21% peracetic acid (0.022 mole) was added within 25 minutes. After an additional 2 hours a t 0" the mixture was allowed to warm to room temperature. After 1 hour a t 25", the mixture was again cooled, the precipitate filtered, and recrystallized from ethyl acetate to give 5.8 grams (81%) of V(R = C,) (m.p. 10,3-25"). Anal. Calcd. for C2(,H4?03S: C, 66.26; H , 11.67; S,8.82. Found: C, 66.44; H , 11.87; S,8.60. Bis(2-hydroxydecyl) Sulfone. A mixture of 1.8 grams of bis(2-hydroxydecyl) sulfoxide ( 5 mmoles), 50 ml. of ethyl acetate, and 3.6 grams of 21'; peracetic acid (10 mmoles) was stirred a t room temperature and allowed to stand over the weekend. After cooling, the white solid was filtered (m.p. 115-23") and recrystallized from ethyl acetate to give 805 VI ( R = C,) (m.p. 120-25'). Anal. Calcd. for C20H,104S:C, 63.44; H , 11.18; S, 8.47. Found: C, 63.70; H , 11.31; S, 8.29. 1-Dimethylamino-2-olctanethiol. A mixture of 21.8 grams of 1,2-epithiooctane (0.15 mole), 50 ml. of benzene, and 9 to 13.5 grams of dimethylamine (0.2 to 0.3 mole) was
sealed in a borosilicate glass tube and heated a t 100" for 4 hours with rocking. The contents of the tube were then distilled to give 25.5 grams (90%) of VI1 (R = C8), (b.p. 53-54" a t 0.2 nim., n: 1.4640). Anal. Calcd. for CI0H2&iS: C, 63.41; H, 12.24; N , 7.40; S, 16.93. Found: C, 63.61; H, 12.37; N , 7.28; S, 16.76. 1-Methylamino-2-dodecanethiol.A mixture of 20 grams of 1,2-epithiododecane (0.10 mole), 50 ml. of benzene, and 7 grams of methylamine (0.25 mole) was sealed in a borosilicate glass tube and heated a t 100" for 2 hours and a t 150" for 2 hours. The benzene was removed in vacuo and the remaining white solid (25.5 grams, m.p. 48-54") was recrystallized from pentane to give 15.7 grams (68%) of VI11 (R = Clo) (m.p. 55--56"). Anal. Calcd. for CI3H1&S: C , 67.47; H , 12.63; N , 6.05; S, 13.83. Found: C, 67.49; H , 12.92; N, 6.00; S, - . Polyepisulfide Formation in Presence of Methylamine
A mixture of 10.0 grams of 1,2-epithiodecane (0.058 mole), 50 ml. of ethanol, and 3 grams of methylamine was refluxed (dry ice condenser) for 1.5 hours. K O volatile products could be detected by VPC of the reaction mixture. Evaporation of the solvent in vacuo left 10.3 grams of a viscous oil which did not, contain nitrogen. Anal. Calcd. for CIOH2,,S: C, 69.7; H. 11.7; S, 18.6. Found: C , 69.3; H, 12.2; S, - . Mol. wt. found: 795. Polyepisulfide Formation in Presence of Ammonia
A mixture of 14.4 grams of 1,2-epithiooctane (0.1 mole), 150 ml. of ethanol, and 17.0 grams of anhydrous ammonia was stirred a t 16" to 32" for 47 hours. After this time, a VPC sample indicated that most of the episulfide had disappeared; however, no product peak could be observed. Removal of the solvent under reduced pressure left 14.0 grams of a viscous oil. Anal. Calcd. for (C8H16S),:C, 66.7; H, 11.1; S, 22.2; N , 0. Found: C, 65.5; H, 11.4; S, 21.7; K, 0.6. Mol. wt. found: 2144 (x = -15). Acknowledgment
I am grateful to W. T. Pace for N M R spectra and their interpretation and to R . B. James for skillful laboratory assistance. Literature Cited
Bordwell, F. G., Andersen, H. M., J . A m . Chem. Soc. 75, 4959 (1953). Braz, G . I., J . Gen. Chem. 21, 757 (1951). Culvenor, C. C. J., Davies, W., Heath, N . S.,J . Chem. SOC.1949, 278. Culvenor, C. C . J., Davies, W., Savige, W. E., J . Chem. Soc. 1952, 4480. Delepine, M., Bull. SOC.Chim. Frunce 27, 740 (1920a). Delepine, M., Compt. Rend. 171, 36 (1920b). Delepine M., Eschenbrenner, S., Bull. SOC.Chim. France 33, 705 (1923). Ettlinger, M. G., J . A m . Chem. SOC.72, 4792 (1950). Goodman, L., Reist E. J., in Kharasch, N., Meyers, C. Y., "The Chemistry of Organic Sulfur Compounds," Vol. 11, pp. 93--113, Pergamon Press, London, 1966. Gould, E. S., "Mechanism and Structure in Organic Chemistry," p. 292, Holt, Rinehart, and Winston, S e w York, 1959. Hansen, B., Acta Chem. Scund. 13, 151 (1959). Kaufmann, H. P., Schickel, R., Fette-Seiien-Anstiichmittel 65 (No. lo), 851 (1963). Moore, C. G., Porter, M., J . Chem. SOC.1958, 2062. VOL. 8 NO. 4 D E C E M B E R 1969
419
Oddon, A., Wylde, J., Bull. SOC.Chim. France 1967, 1603. Reppe, W., Nicolai, F., Ger. Patent 631,016 (June 13, 1936). Schoenberg, A., in Houben, J., Weyl, T., “Methoden der Organischen Chemie,” Band IX, pp. 149 ff, Georg Thieme Verlag, Stuttgart, 1955. Schulz, H. S., Freyermuth, H . B., Buc, S. R., J . Org. Chem. 28, 1140 (1963); and references cited. Snyder, H., Stewart, J., Ziegler, J., J . A m . Chem. SOC. 69, 2672 (1947).
Staudinger, H., Siegwart, J., Helu. Chim. Acta 3, 833 (1920). Swern, D., Billen, G. N., Scanlan, J. T., J . A m . Chem. SOC.68, 1504 (1946). Umbach, W., Mehren, R., Stein, W., Fette-SeifenAnstrichmittel 71, (KO. 3), 199 (1969). Van Tamelen, E. E., J . A m . Chem. SOC.73, 3444 (1951). RECEIVED for review February 26, 1969 ACCEPTED July 19, 1969
AROMATIC ACID ANHYDRIDES BY A DIRECT OXIDATION PROCESS M I C H A E L
A .
T O B I A S
A N D
W A R R E N
W .
K A E D I N G
Research and Development Laboratories, Mobil Chemical Co., Edison, N . J . 0881 7 A novel process for the preparation of aromatic anhydrides involves direct oxidation of the corresponding methyl-substituted aromatic hydrocarbon with oxygen in the liquid phase at atmospheric pressure. Aromatic anhydrides have been produced from the xylenes and mesitylene in 20% yields. Coproducts are the corresponding monobasic acids and substituted benzyl esters.
ANHYDRIDES of carboxylic
acids possess physical and chemical characteristics which make then more attractive industrial intermediates than their parent carboxylic acids. They are usually lower melting and are more soluble in common solvents than their corresponding free acids, and when used for the production of polyesters they react with alcohols with a significant enhancement in rate and produce only half as much water as the carboxylic acids from which they are derived. Acetic anhydride is the only compound of this class which is prepared on an industrial scale by a liquid phase process. Ketene, prepared from acetic acid or acetone, reacts with acetic acid to form the anhydride, or an alternate method is used which involves the autoxidation of acetaldehyde. A method has now been developed for the preparation of aromatic acid anhydrides by the direct reaction between certain methyl-substituted benzenes and oxygen. The corresponding monoaldehyde, benzylic ester, and monocarboxylic acid are the major coproducts produced during the oxidation process. Since the monoaldehyde and benzylic ester can be easily autoxidized to the monocarboxylic acid, production of aromatic anhydrides by this method can be visualized as an industrial process integrated with the production of the corresponding free acid. Experimental
General Procedure. The oxidation procedure and method of product isolation were identical for each reaction. The hydrocarbon and catalyst were charged into a tubular glass reactor and brought quickly to reflux. Oxygen was introduced through the bottom of the reaction vessel, and any water formed was removed by a Dean-Stark trap. At the end of the desired oxidation period, the 420
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
reaction mixture was drained from the reactor and allowed to cool overnight. Crystalline acids were removed, washed with pentane, and dried t o constant weight. Any dissolved acid remaining in the hydrocarbon oxidate was removed with aqueous sodium bicarbonate. The acids were determined by gas chromatography of their methyl esters. The remaining neutral hydrocarbon was washed with dilute hydrochloric acid and dried. Unoxidized hydrocarbons, as well as any aldehyde produced, were isolated by distillation a t reduced pressure. The high boiling residue was again washed with aqueous bicarbonate, and an aliquot treated with a reagent prepared from boron trifluoride and methanol. Anhydride and benzylic ester present in this residue were converted to products which were easily analyzed by gas chromatography.
.
0 0
II I1
ArCOCAr
+
I/
C H S O H 2 2ArCOCH3
0
II
o
ArCHzOCAr + C H 3 0 H
BF3
0
/I
ArCOCH3 t
ArCHzOH + ArCH20CH3 All reaction products were identified by infrared and nuclear magnetic resonance spectroscopy. EXAMPLE1. A tubular, glass reaction vessel, 4 x 100 cm., was charged with 500 grams of p-xylene and 100 p.p.m. of cobalt 2-ethylhexanoate. The solution was brought t o reflux and oxygen was introduced through the bottom of the reactor a t a rate of 500 cc. per minute. Vapors which distilled were condensed, the water was separated and removed, and the p-xylene was returned
