Organic 2 Review Problem 157

Organic 2 Review Problem 157 - PREPARATIONS 141 composition...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
PREPARATIONS 141 composition, the material darkening in colour immediately before melting. a- and £-Pentacetylglucose. C 6 H 7 O(O-COCHg) 5 . When glucose is heated with an excess of acetic anhydride in the presence of a catalyst, all five hydroxyl groups are acetylated, and the resulting pen- tacetyl-glucose can clearly exist in two isomeric forms, corresponding to the a and p forms of glucose itself (see Formulae I and II, p. 135). When zinc chloride is used as a catalyst, the a-pentacetylglucose is formed, and when sodium acetate is used, the [i-pentacetylglucose is produced. It is probable that the product in each case contains traces of the other isomeride, which however can be readily eliminated by recrystallisation. (A) a-PENTACETYLGLUCOSE. Required: Zinc chloride, ca. i g.; acetic anhydride, 25 ml.; glucose, 5 g. From a clean, dry stick of zinc chloride, break off a piece weighing roughly i g., crush it quickly into coarse fragments in a mortar, and then add it to 25 ml. of acetic anhydride contained
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/19/2011 for the course CHM 2211 taught by Professor Castalleano during the Fall '06 term at University of Florida.

Ask a homework question - tutors are online