Glyceryl acetate, detection

Glyceryl acetate, which is an artificial ester commonly used in the adulteration of bergamot oil, is detected fairly easily on account of its high solubility in dilute alcohol. The test is carried out as follows Ten c.c. of bergamot oil and 20 c.c. of 5 per cent, alcohol are well shaken in separating funnel, and after the solutions have separated and become clear the watery solution is run off and filtered. Ten c.c. of the filtrate are exactly neutralised with deci-normal alkali, and then 5 c.c. of seminormal alkali run in, and the whole saponified under a reflux condenser for one hour. In the case of pure bergamot oil 0 1 or at most 0 2 c.c. of semi-normal alkali will have been used up by the saponification, whilst each 1 per cent, of glyceryl triacetate present in the oil will be represented by practically 0 5 c.c. of semi-normal alkali. 

It is evident that, in order to obtain accurate results, the method of working must be clearly and minutely adhered to, especially so in view of the fact that the determination of ester by the method of steam distillation is a very valuable indication as to the purity of an oil, serving to detect the fraudulent addition to oils of such esters as diethyl succinate, triethyl citrate, and diethyl oxalate, the free acids of which are nonvolatile in steam. It will not detect glyceryl acetate, terpinyl acetate, nor the esters of coconut oil fatty acids. 

The oil is frequently adulterated with small quantities of castor oil and other oils. These adulterants present no difficulty when present in appreciable amounts, but when present in small quantity are exceedin y difficult to detect. Oils which only just satisfy the minimum requirements as to solubility, specific gravity, optical rotation, and santalol value should be regarded with considerable suspicion. Glyceryl acetate is sometimes used as an adulterant, and is detected by the high ester value of the sample (for which see Vol. II.). Benzyl alcohol is also sometimes used, but this will be indicated by an abnormally high santalol value and also by the distillation results. With pure sandal oil nothing distils below 280" at ordinary pressure (or 150 at 14 mm.), whilst benzyl alcohol distils at a much lower temperature. Cedar-wood oil is indicated by its insolubility in 70 per cent, alcohol, by its low santalol value, and by its high optical rotation. Further, a considerable distillate is obtained below 280 . The so-called West Indian sandal oil (q.v.) is also a somewhat common adulterant, which is easily detected by the alteration of all the constants of the oil, as well as by its decreased solubility and santalol value . 

With the exception, however, of triethyl citrate, nearly all the nonvolatile esters are to a great extent removed mechanicsdly during the evaporation in the oil vapour. To detect, for example, glyceryl acetate, eth oxalate, ethyl tartrate, and ethyl succinate, the evaporation should only be proceeded with until about 10 to 15 per cent, of tRe oil is left in the dish, and this residue tested for the various acids. 

Glyceryl acetate can be detected and estimated in bergamot and lavender oils by its solubility in 5 per cent ethanol. 

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