Identification of Alcohols By Means of the Optical Properties of the Esters of Carbanilic Acid BARTLETT T . DEWEY
AND
NORMAN F. WITT, University of Colorado, Boulder, Colo.
T
H E optical properties of the esters of carbanilic acid were suggested by the authors in a previous paper (1) as a means for identifying alcohols. They studied the esters of fifteen normal primary alcohols and recorded the optical data, and have since prepared and studied twenty-three more esters. The procedures followed were similar to those employed in the previous work. The esters were prepared by the action of phenylisocyanate on the alcohols (obtained from the Eastman Kodak Company, Rochester, K. Y.). The esters were recrystallized from petroleum ether, a portion was then recrystallized from ethanol, and the crystal system, optic sign, sign of elongation, dispersion, and extinction angle were determined (Table I). 411 the compounds so far investigated belong to the monoclinic system. Their optical character is biaxial. It was impossible to obtain values for some of the indices because of the difficulty of obtaining an orientation which would permit the observation of those values. For nine of the compounds, the values of gamma could not be determined because these values were greater than the maximum refractive index obtainable with the potassium mercuric iodide solutions. For these compounds the lower limiting values given in Table I were determined experimentally or calculated from the birefringence. The optical properties of the compounds recrystallized from ethanol checked with those observed when the compounds were recrystallized from petroleum ether. The crystals from ethanol are larger and better formed, and give clearer interference figures. The additional recrystallization is especially valuable for those esters which have low solubility in petroleum ether. The crystals of glyceryl carbanilate were so poorly formed even after repeated recrystallizations that determination of the optical properties was impossible. In confirming the identity of terpineol, ethylene bromohydrin, ethylene chlorohydrin, and menthol, the crystals of the esters should be oriented Kith the long direction more nearly parallel to the 3 o’clock-9 o’clock direction in the polarizing microscope while the value for beta is observed. Alpha or gamma is found when the long direction of these crystals is
more nearly parallel to the 6 o’clock-12 o’clock direction. For all others these orientations are the reverse. The optical orientation should be established by means of an interference figure before observing the values for alpha or gamma. The identification of some alcohols by means of certain optical properties of their carbanilates has been found possible, even when the refractive indices are identical or nearly so. It is poPsible to distinguish bornyl carbanilate from isoamyl carbanilate by their dispersion. The refractive indices of crystals cf the urethan prepared from ethylene chlorohydrin and those of diphenyl urea, which is formed when water is present, lie very close together. However, crystals of diphenyl urea shoiy an interference color of a gray of a high order. Beveled edges show many bands of color. Thin crystals do not show intense polarization colors. Khen a melt under a cover glass is prepared, the polarization colors are not intense, and interference figures usually show only the dark isogyres. Crystals of the ethylene chlorohydrin carbanilate recrystallized from petroleum ether or rapidly precipitated from hot ethanol solutions show slightly more vivid polarization colors. The crystals obtained by slow evaporation of the solvent from ethanol solutions or from fusion of the material under a cover glass exhibit intense polarization colors. The interference figures show colored bands in addition to the dark isogyres. The components of mixtures of alcohols may be identified by the procedure suggested in the previous paper. Twelve binary mixtures of alcohols in equal proportions were used in preparing carbanilates. The resulting crystalline mixtures were composed of two kinds of crystals, each of which exhibited the same optical properties which it possessed when prepared from the corresponding pure alcohol. The only exception was that of the ethyl and methyl mixture previously reported. Frequently some characteristic serves to indicate the identity of the individual crystal. In a mixture of 3-methylcyclohexanol carbanilate and 4-methylcyclohexanol carbanilate, the former can be quickly distinguished, for its crystals are optically negative while those cf the latter are optically positive. Confirmation is obtained by determination of the refractive indices. In the preparation and recrystallization of carbanilates from a mixture of alcohols, care must OF ESTERSOF CARBANLIC ACID TABLE I. OPTICALPROPERTIES be used to prevent the loss of one of Melting ExtincElonthe components; otherwise the result P:int, tion Optic Refractive Indices gaDiaperwould indicate a pure alcohol instead of Ester C. Angle Sign Alpha Beta Gamma tion sion * a mixture. Allyl 25 1.507 1.586 1,659 Y > P * Isoamyl 10 1.482 1.560 1.626 Y > P * Borneol 1.561 138 30 1.621 None Summary * 1:4i1 Isobutvl 1.572 82 1.656 1s Y > F * 1.541 76 5 Cetyl 1.610 Y > P The optical crystallographic data for * Cinnamyl 1.589 89 10 1: 530 >1.718 P > Y * 32 Cyclohexanol 1.632 83 1.487 >1.775 twenty-three esters of carbanilic acid P > Y * Diethylcarbinol 1.568 45 4s 1.499 1.616 7 2 P have been determined and compared 7 Ethylene bromohydrin 1.665 1.595 76 >1.718 - PP >> YY 27 Ethylene chlorohydrin 1.628 1.583 51 >1.718 with data for fifteen esters and for di* Ethylene glycol 1,625 148 7 >1.718 Y > P * Furfuryl 44 15 i:iig 1.599 >1.718 phenyl urea reported in a previous Y > P Menthol 1.573 111 5 1.558 1.597 P > Y paper. The crystallographic and opti* p-hlethoxybenzyl 90 9 1.550 1 ,602 >1.718 P > Y * 3lethylbenzylcarbinol 19 1.5S4 86 1.532 1.651 Y > P cal properties of the esters of carbanilic * 2-Methylcyolohexanol 20 1.575 103 ... 1.698 P > Y * 42 3-3lethylcyclohexano1 1.562 92 1.667 acid are suitable constants for identifyY > P * 4-Methylcyclohexanol 123 11488 1.613 43 >1.738 P > Y ing the alcohol either pure or in mixtures. * Methylisopropylcarbinol 1.558 69 1.492 14 1.617 Y > P
;;
Rlvristyl Isopropyl Terpineol Tetrahydrofur fury1
71 88 112 5s
25 10 34 43
1.542
1.510
1.511 1.570
1.573 1.573 1.607 1,608
1.577 1.616 >1.718
...
648
* * -
*
None
Y > P P > Y P > Y
Literature Cited (1) D e w e y and Witt, IND. ENG. CHEX, ANAL.ED.,12, 459 (1940).
