[posma]

how to determination purity of menthol by titrations
thank's, GBU

[Arkcon]

Now that's a tough one, I suppose it's OH group is a mild acid, but under what conditions, and with what indicator would you titrate it at?  It doesn't have any other functional groups, so there's not much else to do.  Maybe you'd try spectrophotometric quantitation?

[chiralic]

Hello Posma:

Read this information:

Micro-estimation of Menthol, Menthone and Menthyl-esters in the Essential Oils of Mentha. H. Ullrich and M. Schneider. (HoPPe-Seyler's 2. phys. Chem., 1936, 245, 181-184.)

The oil is obtained from the plant or drug by steam distillation in Clavenger's apparatus in a paraffin bath at 130'-140". The time of distillation varies from 45 to 60 minutes according to the amount of material used. The original apparatus has been modified to include a
burette, having a scale divided to 0.001 ml., below the usual micro-burette. At the end of the distillation the apparatus is allowed to cool and, by running off the water slowly, the oil is transferred to the micro-burette and its volume ascertained. Although there is practically no loss, a correction may be necessary, and this is easily determined. The use of this method necessitates only 1 or 2 g. of material and the accuracy is equal to that with much greater amounts of material. The assay of menthol and menthone by determination of their redox potential is only applicable to chemically pure substances, as other compounds present in the oil have their own effect on the electrodes. In the determination of menthone, the hydroxylamine method of Bennett and Salamon (ANALYST1, 927, 52, 693) is combined with Rehberg's micro-titration method (Biochem. J., 1925, 19, 270), and 0.1 N alcoholic potassium hydroxide is used instead of the usual 0.5 AT solution.
Menthol is oxidised to menthone with chrom-sulphuric acid, as described by Beckmann (Annulen, 1888,250, 324), and is then determined by the Eiydroxylamine method. For the determination of the menthyl esters, the oil is saponified on a water-bath, in a 25-ml. flask connected by a ground-glass joint with an air-condenser.

The excess potassium hydroxide is titrated with 0-1 N sulphuric acid
solution, and the amount used up is calculated to menthyl esters. Hence in an assay of peppermint oil, the menthone is determined direct as such, the menthol is oxidised to menthone which is again determined, and the ester-content is obtained by saponification.

Also, check it out these links:

Quantitative determination of alcohols in essential oils
Flavour and Fragrance Journal Volume 4, Issue 4 , Pages 233 - 234
http://www3.interscience.wiley.com/cgi-bin/abstract/112600096/ABSTRACT

Photocolorimetric determination of menthol in oil and tincture of peppermint
Pharmaceutical Chemistry Journal. Volume 16, Number 1 / 1982/ Pages 68-70
http://www.springerlink.com/content/r110500t0j838330/

Regards,

Chiralic