Irvine-Purdie methylation

The Irvine-Purdie methylation (also Purdie methylation ) is a name reaction in organic chemistry , which was first described in 1903 by James Irvine and Thomas Purdie . The reaction is a methylation of carbohydrates with iodomethane and silver (I) oxide .

Overview reaction

In the Irvine-Purdie methylation, a methyl glycoside is first completely methylated with iodomethane and silver (I) oxide, so that the intermediate product contains ether groups instead of the hydroxide groups . Subsequent hydrolysis removes the anomeric alkyl group with the introduction of a hydroxide group. The reaction is often carried out in neutral solvents under mild conditions and can give products with almost quantitative yield .

Reaction mechanism

The addition of iodomethane and silver (I) oxide to compound 1 leads to nucleophilic substitution taking place with formation of compound 2 , which has an ether group instead of a hydroxide group. Silver iodide and water are produced as by-products .

Compound 2 is completely methylated by further addition of hydrogen iodide and silver (I) oxide . To the resulting compound 3 is hydrochloric acid whereby the anomeric ether group to form the given Intermediates, 4 and removal of methanol is removed and replaced with subsequent hydrolysis by an hydroxy group. The reaction product 5 is obtained with elimination of hydrochloric acid .

modification

The Irvine-Purdie methylation was modified in 1915 by Walter Norman Haworth . In the so-called Haworth methylation, dimethyl sulfate and sodium hydroxide solution are used instead of iodomethane and silver (I) oxide for the alkylation of sugars. This enables a more cost-effective synthesis. However, the Haworth methylation has the disadvantage that it is time-consuming, gives relatively low yields and the work-up of the reaction product is difficult. Edward West and Raymond Holden modified the reaction further in 1934 and added a carbon tetrachloride solution in the presence of a more highly concentrated sodium hydroxide solution to the sugar to be methylated.

application

The reaction is generally used to produce methylated sugars. These are often used as reference compounds in carbohydrate chemistry. Methylations play an important role, especially for the structure elucidation of polysaccharides , since, for example, methylation of the same polysaccharide can provide more precise information about the substance using different techniques.

Individual evidence

1. ↑ James C. Irvine, Thomas Purdie: C. — The alkylation of sugars . In: Journal of the Chemical Society, Transactions . tape 83 , January 1, 1903, p. 1021-1037 , doi : 10.1039 / CT9038301021 .
2. ↑ ^{a b c d} Zerong Wang: Irvine-Purdie methylation . In: Comprehensive Organic Name Reactions and Reagents . John Wiley & Sons, Inc., Hoboken, NJ, USA 2010, ISBN 978-0-470-63885-9 , pp. 1526-1529 , doi : 10.1002 / 9780470638859.conrr341 .
3. ^ Walter Norman Haworth: III. — A new method of preparing alkylated sugars . In: Journal of the Chemical Society, Transactions . tape 107 , January 1, 1915, p. 8-16 , doi : 10.1039 / CT9150700008 .
4. ↑ ^{a b} B. Clifford Hendricks, Robert E. Rundle: The Methylation of Sugars . In: Journal of the American Chemical Society . tape 60 , no. 10 , October 1, 1938, p. 2563-2564 , doi : 10.1021 / ja01277a504 .
5. ↑ NWH Cheetham, RJ McIlory: polysaccharides methylation studies . In: Carbohydrate Research . tape 11 , no. 2 , October 1, 1969, p. 187-191 , doi : 10.1016 / S0008-6215 (00) 80073-7 .