Haworth method

Substituted phenanthrenes are obtained by modifying the basic scheme in the ways already described for the Haworth method (Sec. 30.14). 

Apply the Haworth method to the synthesis of the foRowing, starting from naphthalene or a monosubstituted naphtfaalenev... 

NRRL B-742 dextran may be artifactual structures, resulting from incomplete methylation of this highly branched polysaccharide. Dextrans have been methylated most frequently by the Haworth method, " and by procedures that employ sodium and methyl iodide in liquid ammonia. " " Rapid methylation of dextrans has been achieved " through the use of the Hakomori procedure, which utilizes methyl sulfoxide as solvent for the dextran. Careful control of the reaction temperature would, however, appear to be essential when a dextran is methylated in this solvent, as hot methyl sulfoxide has been reported to depolymerize native dextrans." ... 

Total methylation of all available hydroxyl groups in a polysaccharide generally requires initial methylation by the Haworth method (dimethyl sulfate and aqueous sodium hydroxide) to introduce sufficient lipophilic... 

A further example is given below illustrating the use of a dibasic anhydride (succinic anhydride) the succinoylation reaction is a valuable one since it leads to aroyl carboxylic acids and ultimately to polynuclear hydrocarbons. This general scheme of synthesis of substituted hydrocarbons through the use of succinic anhydride is sometimes called the Haworth reaction. Thus a-tetralone (see below) may be reduced by the Clemmensen method to tetralin (tetrahydronaphthalene) and the latter converted into naphthalene either catal3d.ically or by means of sulphur or selenium (compare Section, VI,33). 

Friedel-Crafts Acylation. The Friedel-Crafts acylation procedure is the most important method for preparing aromatic ketones and thein derivatives. Acetyl chloride (acetic anhydride) reacts with benzene ia the presence of aluminum chloride or acid catalysts to produce acetophenone [98-86-2], CgHgO (1-phenylethanone). Benzene can also be condensed with dicarboxyHc acid anhydrides to yield benzoyl derivatives of carboxyHc acids. These benzoyl derivatives are often used for constmcting polycycHc molecules (Haworth reaction). For example, benzene reacts with succinic anhydride ia the presence of aluminum chloride to produce P-benzoylpropionic acid [2051-95-8] which is converted iato a-tetralone [529-34-0] (30). 

This method, utilized simultaneously by Reichstein2 and by Haworth and coworkers3 in the first synthesis of d- or L-ascorbic acid, can be illustrated in detail by reference to the preparation of D-glucoascorbic acid (XV).3... 

Both methods of approach moreover proved that a series of methylated derivatives of D-glucosamine described by Cutler, Haworth and Peat,14 and most useful as reference compounds in this field, were all of the pyranose configuration. Further proof of the pyranose structure of methyl D-glucosaminide and methyl N-acetyl-D-glucosaminide was pro-... 

Methylgraminin was obtained as a colorless sirup by the method of Haworth and Streight.24 Hydrolysis of the methyl derivative gave a mixture of di-, tri-, and tetramethyl-D-fructoses that were separated after conversion to benzoyl derivatives. The authors conclude that these partially methylated D-fructoses are present in the ratios 1 1 1 or 1 2 1. 

For the methylation of the free hydroxyl groups of a partially esterified carbohydrate, e.g., of a partially acetylated compound, only the Purdie method is available. Although liquid ammonia does not react with esters at — 70°C., there is a danger of saponification if the temperature of the reaction mixture is allowed to rise before all the ammonia has been removed. The aqueous alkali employed in the methods of Haworth or Menzies will, of course, remove ester groups by hydrolysis. 

Methods of Formation.—The first sample of 4,6-dimethyl-D-glucose, prepared by Haworth and Sedgwick97 in 1926, came, together with tri-and tetramethylglucoses, from the incomplete methylation of glucose with methyl sulfate and sodium hydroxide. It was not characterized until about a decade later, when it was isolated by Bell and Synge98 from another source. 

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