[CONTRIBUTION FROM
NOYESCHEMICAL LABORATORY, UNIVERSITY
OF ILLINOIS]
T H E REACTION OF ANISOLE WITH 1,1,l-TRICHLOR0-2-METHYL2-PROPENE CHARLES
C.
PRICE
AND
HOWARD D. MARSHALL
Received July 22, 1945
The correlation of the effect of groups in orienting substitution in the benzene ring and addition to the olefinic double bond has been pointed out by Robinson (1). Those groups which orient ortho-para in benzene, direct addition according to Markownikoff’s rule; those groups which orient meta in benzene, direct addition in opposition to Markownikoff’s rule. The report of Kharasch, Rossin, and Fields (2) that 1,1,1,2-tetrachloropropane (11)is formed by addition of hydrogen chloride to 1 ,1,l-trichloro-2-propene (I) appears to be one of the few exceptions to this generalization. In view of C&CCH=CH2 I
+ HC1
C13CCHClCH, I1
the difficulty with which this olefin reacted with hydrogen halides, we have continued a similar investigation which was in progress a t the time the work of Kharasch, Rossin, and Fields was published. The homologous olefin, 1,1,l-trichloro-2-methyl-2-propene(111) (3), has shown the same remarkable resistance to any characteristic addition reaction at the double bond.
OH
I
CLCCCHa
P2Os
quinoline
C&CC=CHs I
The trichloroisobutylene (111) was resistant t o attack by bromine and by potassium permanganate and did not dissolve in concentrated sulfuric acid. The addition of hydrogen chloride or bromide was not practicable because of the ease with which this olefin undergoes an allylic rearrangement (3). ClsCC=CHz
I
Hf
--+
CH3 I11
ClzC=CCH,Cl
I
CHa IV
The reaction of anisole with the trichloroisobutylene (111), using hydrogen fluoride as a catalyst, proceeded smoothly. On the basis of analysis, oxidation to p-anisic acid, and chemical properties, the product has been assigned the structure of 1,1-dichloro-2-methyl-3-p-anisyl-l-propene (V). 532
533
ANISOLE AND TRICHLOROMETHYLPROPCNE
Compound V gave no precipitate when heated in alcoholic silver nitrate solution and was attacked by bromine in carbon tetrachloride and by permanganate only very slowly. The allylic rearrangement product of 111, isomer IV, formed from I11 in hydrogen fluoride, was found t o give only very small yields (less than 5%) of V when treated with anisole and hydrogen fluoride under the same conditions. The formation of V from I11 may thkrefore be interpreted as a direct addition of anisole to the double bond of I11 in opposition to Markon-nikoff's rule. This addition product will yield V by loss of hydrogen chloride.
- +
CHaO- /-\
An alternative explanation which cannot be disregarded involves the possibility of the dissociation of I11 t o give a resonating ion common to both the allylic reaarangement and the Friedel-Crafts reaction. CH2=CCCb
I
HF + + CH2=CCC12
CH8 I11
IV
-
C H ~ O ~ C H ~ C = C+ -HT C Ic ~ a
I
CH3
I
+ C1-
CH3
I CsHs 0CH,
H @ I/ H
oa /
CH2 C=CClr
I
CH3 It has been pointed out by Hughes (4)that ionization of this sort is favored by accumulation of chlorine in the similarly-situated trichloromethyl group of benzotrichloride.
534
C. C. PRICE AND H. D. MARSHALL EXPERIMENT.4L
Dehydration of chloretone hydrate. The chloretone used was obtained from Eastman Kodak Company, and was in the form of the monohydrate. The water of hydration was removed by dissolving the compound in a moderate excess of either benzene or ether, and drying with solid potassium carbonate. The benzene (or ether) was then distilled, and the anhydrous chloretone left was allowed to solidify, or was distilled. It usually melted at 95-96". Distillation of the chloretone did not seem to offer any particular advantages. Dehydration of chloretone. Twenty-one grams of anhydrous chloretone was dissolved in 29 cc. of quinoline (2 moles)' in a 500-cc. round-bottomed flask fitted with a delivery tube and a water-cooled condenser set downward for distillation. Fifty-two grams of phosphorus pentoxide2 was added and mixed well with the quinoline solution. The flask was placed in an oil-bath a t a temperature between 135" and 145". The oil-bath was heated rapidly to 155". The contents of the flask swelled, filled the flask completely, and sometimes even the delivery tube. The swelling helped to sweep over the distillate, which consistcd of a mixture of trichloroisobutylene (HI),the allylic rearrangement product (IV), a-chloroisobutyryl chloride: and unreacted chloretone. The dehydration reaction required five to ten minutes. Under these conditions, 4 to 5 cc. of distillate, sometimes blue-colored, was obtained; this corresponds to 30 to 35% of the theoretical yield of trichloroisobutylene (111). The distillates of several runs were combined and washed with dilute, aqueous potassium carbonate until all the a-chloroisobutyryl chloride was hydrolyzed and neutralized. The product was then dried with solid potassium carbonate, and fractionated under diminished pressure. The main fraction distilled at 42-44' (29-30 mm.), and the second (small and sometimes negligible) distilled at 62-64' (29-30 mm.). Any residue is presumably unchanged chloretone. Larger yields of distillate have been obtained by using somewhat larger quantities of starting materials. For example, 25 g. of chloretone, 60 g. of phosphorus pentoxide, and 34 cc. of quinoline gave a 43% yield. On being heated rapidly, however, these larger quantities may stop up the delivery tube, and cause a minor explosion. It is believed that larger yields of trichloroisobutylene could be obtained if the swelling of the reaction mixture could be reduced appreciably, or eliminated. Undoubtedly, a large portion of trichloroisobutylene simply remains in the flask, and is entrapped in the hard, insoluble residue. Allylic rearrangement of trichloroisobutylene (ZZZ) ( 6 ) . Approximately 10 cc. of trichloroisobutylene was added to 5 g. of phosphorus pentachloride in a 200-cc. round-bottomed flask fitted with a water-cooled condenser and a calcium chloride drying tube. After heating on a steam-bath for four hours, the reaction mixt'ure was poured into cold, dilute potassium carbonate solution to hydrolyze and neutralize the phosphorus pentachloride. The organic material was separated, dissolved in ether, washed with water, and distilled under atmospheric pressure. About 8 cc. (80%) of material boiling a t 153-156" was obtained. After redistillation, it boiled a t 154-157"; n: 1.4965; d: 1.332. The constants reported by Jacob (3) were: b.p. 155'; n: 1.497; d p 1.335. Reaction of anisole and trichloroisobutylene (111) in the presence of hydrogen fluoride. Trichloroisobutylene (5.5 g.) was mixed with 5.5 g. of anisole (1.5 equivalents), and approximately 40 cc. of hydrogen fluoride in a copper beaker cooled in an ice-bath. The mixture was mechanically stirred with a piece of bent copper wire, and was allowed to stand overnight. It was poured into about 60 cc. of water, made slightly alkaline with potassium 1 By using two moles of organic base, rather than one equivalent of dimethylaniline (3), much less allylic rearrangement occurred during the dehydration. 2 Merck's phosphorus pentoxide was used, principally because i t was much more dense than several other brands available. I t was more easily handled and gave much more satisfactory results. Its presence was estab3 Less than 5% of the distillate was a-chloroisobutyryl chloride. lished by treating unwashed distillate with aniline. The melting point of the a-chioroisobutyranilide (m.p. 69.5-T0.5") agreed with that reported by Kharasch and Brown (5).
AXISOLE AND TRICHLOROMETHYLPROPENE
535
carbonate, and extracted with two 40-cc. portions of ether, which yielded six grams of material after the ether was distilled. On distillation, 3.0 g. (387,) of l , l-dichloro-2-methyl-3p-anisyl-1-propene (V) was obtained as a somewhat yellow liquid which boiled at 124-126" (4 mm.); ng 1.5518. I t had a characteristic, pleasant odor. An analytical sample had the following properties: n: 1.5504; d y 1.210. Anal. Calc'd for CllH12Cl20:C, 57.16; H, 5.23; ME, 60.30. Found: C, 57.50; H , 5.20; It$;, 60.90. Chromic acid oxidation of V. The calculated amount of chromic acid (1.00 6.) dissolved in about 10 cc. of glacial acetic acid, was added to 1.73 g. of (111) dissolved in about 10 cc. of glacial acetic acid. The mixture was heated a t about 70" for about twelve hours, a t 95100" for about thirty hours, and then boiled under reflux for four hours. During this time, about 5 cc. of acetic acid was added to replace that lost by evaporation. A t the conclusion of the refluxing, the red color of chromic acid was only faintly visible by transmitted light. The mixture was poured into 100 cc. of water, and extracted with three 40-cc. portions of ether. The ether extract was washed with two 40-cc. portions of water, and then dilute potassium carbonate. The potassium carbonate solution yielded, on acidification, p-anisic acid (about 0.1 g.), m.p. 180-182", corr. Reactzon of anisole and the allylic rearrangement isomer ( I V ) in the presence of hydrogen juorzde. Three separate runs were carried out with the allylic isomer (IV). The experimental prcicedure was the same as that with trichloroisobutylene (111), except that the samples were all slightly larger: 8.5 g., 6.5 g., and 6.0 g. The yields of V were, respectively, 0.5 g., 0.5 g., and 0.2 g., all less than 6% of the theoretical yield. The 6.0-g. sample was the most carefdly purified. The other samples might have contained up to 10% of trichloroisobutylene (111). Reaction of trichloroisobutylene ( I I I ) and hydrogen .fluoride. Fifteen grams of trichloroisobutylene (111) was mixed with about 30 cc. of hydrogen fluoride in a copper beaker cooled in an ice-bath, and mechanically stirred with a piece of bent copper wire for about fonr hours. A t first, the reaction mixture turned yellow, but the color disappeared after a short while. Usually the hydrogen fluoride fumes precluded observation of the reaction. The reaction mixture was poured into ice-water and the hydrofluoric acid wm neutralized with a slight excess of potassium carbonate. After standing overnight, the organic liquid was taken up in ether, and dried with solid potassium carbonate. The ether was distilled off and the residue fractionated. About 4.5 cc. of material was obtained in two fractions, with refractive indices of 1.4972 and 1.4986, and specific gravities of 1.333 and 1.336. This corresponds to a 40% yield of allylic rearrangement product. About 2 cc. of a third fraction, evidently a dimer or trimer, was obtained; b.p. 109-113" (3 mm.), nz 1.5354. SUMMARY
The double bond of 1, 1, l-trichloro-2-methyl-2-propene is remarkably inert. This olefin is not attacked by bromine in carbon tetrachloride or by aqueous potassium permanganate and is insoluble in concentrated sulfuric acid. It reacts readily with anisole in the presence of hydrogen fluoride t o yield 1,1-dichloro-2-methyl-3-p-anisyl- 1-propene. URBANA, ILL.
REFERENCES (1) SMITH,Chem. and I n d . , 67, 461 (1938); PRICE, COYNER, A N D DETAR,J . Am. Chem. SOC., 63, 2796 (1941); PRICE,Chem. Rev., 29, 37 (1941). (2) KHARAE~CB, ROSSIN,A N D FIELDS, J . Am. Chem. SOC., 63, 2558 (1941). (3) JACOB, Bull. S O C . chim, (51, 7, 581 (1940). Trans. Faraday soc., 37, 620 (1941). (4) HUGHES, (5) KHARAECR A N D BROWN, J . A m . Chem. SOC.,62,928 (1940). (6) KIRRMANN AND JACOB, Bull. SOC. chim., [5], 7 , 586 (1940).
