[CONTRrBUTION FROM THE PRICK CHEMICAL LABORATORY OF PRINCETON UNIVERSITY]
T H E PREPARATION AND OPTICAL ROTATION OF DEUTERO-
METHYLMETHYLPHENYLMETHANE ROBERT L. BURWELL, JR., FRITZ HUMMEL,
AND
EVERETT S. WALLIS
Received August 10, 1956; revised October 2, 1956
The preparation of deuterium oxide has made it possible to investigate experimentally the problem of producing optically active organic compounds, the asymmetry of which is due to certain inherent differences which exist between hydrogen and deuterium. Porter’ hoped to prepare compounds of the type, RR’CHD, in optically active modifications by means of the Grignard reaction, but this method was doomed to failure since Pickard and Kenyon2 had previously shown that racemization accompanied the preparation of the Grignard reagent from optically active halides of the type, RR’CHX. A different approach to the problem has been made by H. Erlenmeyer and H. G a ~ t n e r . Their ~ experiments, however, failed to produce positive evidence. Recently Biilman, Jensen and Knuth4have published experimental work in which they claim that they have been successful in preparing an optically active 2-deuterocamphane.* CH3
I
1 ‘ I
CH2-C-
CHD
CH3-(jJ-CHa
CH2-C
I
-CH2
H PORTER, J . Am. Chem. SOC.,67,1436 (1935). PICKARD AND KENYON, J . Chem. SOC.,99,65 (1911);see also WALLISAND ADAMS, J . Am. Chem. SOC.,66,3838 (1933). 8 ERLENMEYER AND GHRTNER, HeZv. Chim. Acta, 19,331 (1936). 4 BIILMAN, JENSEN,AND KNUTH,Ber., 69,32 (1936). * Since this manuscript was sent t o the Editor there has appeared an article by BIILMAN, JENSEN,AND BAK,Ber., 69, 1947 (1936), which shows that the conclusions in the paper cited above are untenable. A paper by LEFFLERAND ADAMS,J . Am. Chem. floc., 68, 1555 (1936),also discusses these results. 332 1 f
PREPARATION OF DEUTEROMETHYLMETHYLPHENYLMETHANE
333
Clemo and McQuillens have described experiments which seem to prove that optically active compounds of the type, CR(R’D)XY, can be prepared.. Their results justify their claim that they “have proved the resolvability of the base,”
H D~c~-C-C~H~
I
“2
During the last two years we have also been engaged on this problem, and we now wish to report the results of certain experiments carried out on a compound different in type, from those studied by other investigators. This paper reports the upper limit of the optical rotation of a deuteromet hylmet hylphenylmet hane ,
prepared from the Grignard reagent of d-2-bromo-l-methyl-l-phenylethane, [a]:5 13.75,* and deuterium oxide. A sixty per cent. ether solution of the deuterocumene thus prepared showed no observable rotation. A determination, however, of the rotatory 0.019, power of a sample of the pure hydrocarbon gave a value of [CY] pure liquid, l-dm. tube (average of eleven readings; maximum deviation from the mean, 0.011). Samples of this cumene prepared by the action of water, and of deuterium oxide on the Grignard reagent of a bromidei of rotation [CY], - 1.9 showed no observable rotation. In submitting these results for publication we do not claim to have proved beyond question that d-deuteromethylmethylphenylmethane has an observable rotation, inasmuch as the value obtained, 0.019, is nearly within the experimental error. We do state, however, that our experiments clearly show that the maximum rotation of compounds of this type is very small. In this respect the results are in agreement with the theoretical considerations of Boys,6 which predict a small rotation for a
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6
CLEMO AND MCQUILLEN, J . Chem. SOC.,1936,808.
* COHEN,MARSHALL AND WOODMAN, J . Chem. SOC.,107,899 (1915), have reported the value of the rotation of a more completely resolved bromide as [a]:f15.6. t This material was kindly furnished to us by Dr. P. A. Levene, Rockefeller Institute, New York City. 6 BOYS, Proc. Roy. Soc., A144,655 (1934).
334
R. L. BURWELL, JR., F. HUMMEL, AND E. S. WALLIS
compound of the type we have prepared. If one agrees with him that the essential factors determining the value of the rotatory power of a molecule are the effective atomic or group radii of the groups attached to the asymmetric carbon atom, then it is evident that the difference between the effective radii of methyl and deuteromethyl groups is much smaller than between groups commonly causing optical rotation, and hence only a small rotation is to be expected.
FIG.1 EXPERIMENTAL
d-9-Bromo-1-methyl-1-phenylethanewas prepared according to the method of Cohen, Marshall and Woodman (Zoc. cit.) from the corresponding alcohol ([a]: 10.42, pure liquid, 1-dm. tube) b y the action of hydrogen bromide. It had a rotation of [a]: 13.74 (pure liquid, 1-dm. tube). The preparation of the Grignard reagent, and its subsequent reaction with deuterium oxide was carried out in the apparatus illustrated in Fig. 1. The apparatus was constructed of Pyrex glass and satisfactorily held a vacuum of 10-4 mm. of mercury. Bulbs I and I1 each had a capacity of about 20 cc. The tube at the bottom of bulb I1 was marked to indicate a volume of 2 cc. Outlet A from the three-way stopcock led to a McLeod gauge, and a mercury vapor diffusion pump backed by an oil pump. Outlet B led to a source of nitrogen. Tank nitrogen was passed through a tube containing copper wool maintained a t a temperature of 470°, thence through soda lime, calcium chloride, a trap cooled with
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PREPARATION OF DEUTEROMETHYLMETHYLPHENYLMETHANE
335
solid carbon dioxide-toluene mixture, and a trap cooled with liquid air. This purification train was constructed of fused Pyrex tubing. Thus nitrogen admitted to the reaction apparatus was free from oxygen, carbon dioxide, and water vapor. Four-tenths gram of especially prepared magnesium was washed twice with ether and placed in bulb I, which was then sealed to the apparatus. The apparatus was evacuated through outlet A and heated with a free flame to eliminate adsorbed gases. The pumping was continued overnight. Bulb I was cooled with liquid air. Nitrogen was then admitted to the apparatus under a pressure exceeding that of the atmosphere by 2 cm. of mercury. The seal over bulb I was heated and blown out by the nitrogen pressure. A very small crystal of iodine was added to bulb I ; 1.75 cc. of d-2-bromo-I-methyl1-phenylethane and 10 cc. of ether dried over sodium were added by means of especially constructed pipettes, which avoided introduction of light water vapor; the apparatus was then sealed off a t C. Water cooled to 0" was run through the condenser. Reaction began when the temperature of bulb I was allowed to rise to room temperature. Auto-refluxing continued for ten minutes. The refluxing was maintained for an hour by the application of heat. Bulbs I and I1 were then cooled with liquid air and the seal over bulb I1 was blown out;,1.00 cc. of 99.5 per cent. deuterium oxide was inserted into bulb TI; theapparatus was sealed off a t D. The apparatus was evacuated through outlet A , and then the three-way stopcock was closed. The liquid air was removed from bulb 11, and the deuterium oxide distilled into bulb I. Nitrogen was admitted to the apparatus. Reaction took place when bulb I was warmed to room temperature. The contents of bulb I were refluxed for two hours. The volatile contents of bulb I were then distilled into bulb I1 in the same fashion as described above. Nitrogen was admitted to t,he apparatus and bulb I was cut off and cleaned. Phosphorus pentoxide was inserted in bulb I and i t was resealed to the apparatus. The contents of bulb I1 were then distilled into bulb I. The excess of deuterium oxide combined with the P106.Bulbs I and I1 were cooled with liquid air and then the apparatus was evacuated. Bulb I was allowed to warm to room temperature, and the volatile contents of bulb I were distilled into bulb 11. The contents of bulb I1 were distilled hack into bulb I until about 1.75 cc. remained in bulb 11. The distillation was then stopped and nitrogen was admitted. Seal D was opened and the rotation of the contents of bulb IT was determined at 25" in a 1-dm. polarimeter tube. There was no observable rotcttion. One and eight-hundredths grams of this ether solution was distilled in a micro distillation apparatus; 0.64 g. of deuterocumene, b.p. 151-152", was obtained. : (pure The rotation of this pure deuterocumene was then determined: [ C Y ]0.019 liquid, length of tube 1 dm., average of 11 readings, maximum deviation from the mean 0.011). Similar experiments carried out on a bromide, [elD- 1.9,* with deuterium oxide and with water gave a cumene which showed no observable rotation.
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SUMMARY
The preparation of d-deuteromethylmethylphenylmethane has been described. The upper limit of its optical rotation is reported. The experimental results are briefly discussed in connection with certain theoretical considerations of Boys. I'
Kindly furnished by Dr. P. A. Levene, Rockefeller Institute, New York City.
