2-Thio 6-methyluracil

The product is collected on a 4-in. Buchner funnel and is washed with about 200 ml. of cold water in four portions. The solid is permitted to drain (with suction) for several hours and is then transferred to an oven at 70° for more complete drying. The yield of oven-dried 2-thio-6-methyluracil is 98-119 g. (69-84%). This material is sufficiently pure for the desulfurization reaction (Note 2). 

B. 4-Metkyl-6-hydroxypyrimidine. To a hot solution of 10 g. (0.07 mole) of 2-thio-6-methyluracil in 200 ml. of distilled water and 20 ml. of concentrated aqueous ammonia in a 500-ml. round-bottomed flask is added 45 g. (wet paste) of Raney nickel catalyst (Note 3). About 30 ml. of distilled water is used to wash all the nickel catalyst into the reaction flask. The mixture is heated under reflux in a hood for about 1.5 hours. The catalyst is permitted to settle, and the clear solution is decanted and filtered by gravity. The catalyst is washed with two 75-ml. portions of hot water and is discarded (Note 4). The combined filtrate and washings (Note 5) are evaporated to dryness on a steam bath. The residue is placed in an oven at 70° to complete the drying process (Note 6). The yield of crude pyrimidine, m.p. 136-142°, is 7.0-7.2 g. (90-93%). 

Thio-6-methyluracil does not possess a clearly defined melting point but shows marked decomposition above 280°.2... 

Methyl-6-hydroxypyrimidine can be prepared by heating 2,6-dichloro-4-methylpyrimidine with red phosphorus and hy-driodic acid 8 and by treating 2-thio-6-methyluracil with hydrogen peroxide.6 The present synthesis is modeled after the work of Brown,3 who has described the desulfurization of several thiopyrimidines. 

The procedure for the synthesis of 2-thio-6-methyluracil is a modification of the method described by Wheeler and Merriam 7 for the preparation of 2-methylthio-6-methyluracil. 

A. 2-Thio-6-methyluracil. In a 2-1. flask are placed 76 g. (1 mole) of thiourea, 130 g. (1 mole) of commercial ethyl aceto-acetate, 120 g. of commercial sodium methoxide, and 900 ml. of methanol. The reaction mixture is heated gently on the steam bath and is permitted to evaporate to dryness in a hood over a period of about 8 hours. The residue is dissolved in 1 1. of hot water the solution is treated with a few grams of activated carbon and is filtered. The hot filtrate is carefully treated (Note 1) with 120 ml. of glacial acetic acid. The thiouracil precipitates rapidly and is collected on a 4-in. Buchner funnel. The still wet solid filter cake is suspended in a boiling solution of 1 1. of water and 20 ml. of glacial acetic acid. The slurry is stirred and mixed thoroughly to break up lumps and is then refrigerated. 

Hydrogen cyanide, 33, 7 Hydrogen fluoride, catalyst for alkylations, 32, 91 Hydrogen iodide, 31, 32 Hydrogenolysis of 2-thio-6-methyluracil, 35, 81... 

Thio-6-methyluracil. Furfural Nickel Copper chromiuln oxide 100 0 4-Methyl-6-hydroxypyrimidine 3... 

Condensation of 21 with 2-thio-4-methyluracil in the 5-position has been reported.147 The structural assignment of the product was based on analogies.147, 148 Reaction of 19 with l-chloropropane-2,3-diol followed by periodate cleavage affords saccharin-iV-acetaldehyde.149... 

THIO-4-METHYLURACIL see MPW500 THIOMETON see PHI500 THIOMIDIL see MPW500 THIOMONOGLYCOL see MCN250... 

Desulfurization is useful in the synthesis of heterocycles where the desired ring system can be constructed most readily in the form of a suKhydryl derivative. An example is the synthesis of 4-methyl-6-hydroxypyrimidine via2-thio-6-methyluracil. The crude thio derivative was desulfurized with 45 g. (wet paste) of Raney nickel. 

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