AMINO-4-METHYLTHIAZOLE

Seventy-six grains (1 mole) of thiourea is suspended in 200 cc. of water (Note 1) in a 500-cc. flask equipped with a reflux condenser, dropping funnel, and mechanical stirrer. The stirrer is started, and 92.5 g. (1 mole) of chloroacetone (Note 2) is run in during thirty minutes. As the reaction proceeds the thiourea dissolves and the temperature rises. The yellow solution is refluxed for two hours and cooled, and, while the mixture is stirred continuously but not so rapidly as to produce a troublesome emulsion, 200 g. of solid sodium hydroxide is added with cooling. The upper, oily layer is separated in a separatory funnel and the aqueous layer is extracted three times with ether, using a total of 300 cc. (Note 3). The dark red oil is combined with the ethereal extract, and the solution is dried over 30 g. of solid sodium hydroxide and filtered by gravity to remove small amounts of tar. The ether is removed by distillation from a steam bath, and the oil is distilled at reduced pressure. After a very small fore-run, the 2-amino-4-methylthiazole is collected 

The reaction may be conducted without this diluent, but it is then likely to become violent. 

Commercial chloroacetone was distilled and the fraction boiling at 116-122° taken nearly all of this boiled at 118-120°. 

If a precipitate is produced and causes an emulsion, it is well to add ice and water until this dissolves. 

The method given is essentially that of Traumann.1 2-Amino-4-methylthiazole has been prepared also from chloroacetone and ammonium thiocyanate,2 from chloroacetone and ammonium thiocyanate in ammonia water,3 by the action of ammonium thiocyanate on thiocyanoacetone,3 by saponifying and decarboxylating the cyclic ester from ethyl 7-bromoaceto-acetate and thiourea,4 and from thiocyanoacetone and ammonia in absolute ether.5 

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Amino-4 -methylthiazole slowly decomposes on storage to a red viscous mass. It can be stored as the nitrate, which is readily deposited as pink crystals when dilute nitric acid is added to a cold ethanolic solution of the thiazole. The nitrate can be recrystallised from ethanol, although a faint pink colour persists. Alternatively, water can be added dropwise to a boiling suspension of the nitrate in acetone until the solution is just clear charcoal is now added and the solution, when boiled for a short time, filtered and cooled, deposits the colourless crystalline nitrate, m.p. 192-194° (immersed at 185°). The thiazole can be regenerated by decomposing the nitrate with aqueous sodium hydroxide, and extracting the free base with ether as before. 

This reaction, thoroughly studied for 2-aminopyridine (14, 15), has received less attention in the case of the thiazole nucleus. 2-Amino-4-methylthiazole is formed when 4-methylthiazole is heated with sodium amide for 15 hr at 150°C (16). This reaction was used to identify 2-amino-4-butylthiazok (17). 

The mass spectra of 2-aminothiazole and 2-amino-4-methylthiazole are characterized by the following peaks (136). 

Zugravescu et al. (263) showed that ethyl chloroformate reacts on the exocyclic nitrogen of 2-amino-4-methylthiazole to yield the carbamate (101) (Scheme 70) (see also Refs. 264 and 265). With an excess of chloroformate (2 moles for one of the thiazole) under Schotten-Bauman conditions the jV.A -dicarbamate of 2-imino-4-methylthiazoline (102) is obtained (263),... 

Maleic anhydride condenses with 2-aminothiazole-4-carboxylic acid giving the raaleimide 107 (269) another report claims, however, that the reaction of 2-amino-4-methylthiazole with this anhydride gives the N-substituted maleamic acid (108) (Scheme 73) (270). 

Takatori (274) formylated 2-amino-4-methylthiazole with formic acid. When NHj is bubbled for 6 hr into a mixture of 2-amino-4-methyl-thiazole and propionic acid at 100°C, 2-propionamido-4-methylthiazole is obtained (275). 

Vollmann found that the reaction between l-imino-3-amino isoin dolenine (124) and 2-amino-4-methylthiazole is catalyzed by ammonium chloride and involves the exocyclic nitrogen (285). This reaction (Scheme 82) was later used to prepare dyes (286). 

Picryl halides react with 2-amino-4-methylthiazole. Again, the exocyclic nitrogen is the reactive center (288). and the product formed (128) is... 

Amino-4-methylthiazole also gives a complex with Hg(II) that has been used in a gravimetric determination of this metal (366). 

When 2-amino-4-methylthiazole is nitrated under mild conditions, 2-nitramino-4-methylthiazole (180) is isolated (Scheme 114) (16, 194. 374). 

In fuming sulfuric acid (20% oleum) 2 aminothiazole (16. 27. 375. 389) and 2-amino-4-methylthiazole (374. 390) are sulfonated in the 5-position. When this position is substituted as in 2-amino-5-methyl-thiazole (27, 391) very small amounts of 4-sulfonation occur. 

The halogen in the 5-position of 2-aminothiazoles is usually reactive and is used for further reaction (see Chapter V). The reaction may take place in the same medium as thiocyanation (437-440), rhodanation (441). or reaction with NaNO (435). Similarly, a mixture of 2-amino-4-methylthiazole and thiourea in H2O yields 5,5 -thiobis(2-amino-4-methyDthiazole (202) after addition of iodine (Scheme 128) (442). 

Amino-4-phenylthiazole when heated with Raney Ni is reported to yield acetophenone (469). In the course of a general study on reductive cleavage in heterocyclic systems Hoff et al. studied the reaction of 2-amino-4-methylthiazole with Na in liquid ammonia. Two equivalents of Na are necessary to obtain a mixture of 4-methyl-3-thiazoline (240) and... 

Diazo coupling involves the N exocyclic atom of the diazonium salt, which acts as an electrophilic center. The diazonium salts of thiazoles couple with a-naphthol (605). 2-nitroresorcinol (606), pyrocatechol (607-609), 2.6-dihydroxy 4-methyl-5-cyanopyridine (610). and other heteroaromatic compounds (404. 611) (Scheme 188). The rates of coupling between 2-diazothicizolium salts and 2-naphthol-3.6-disulfonic acid were measured spectrophotometrically and found to be slower than that of 2-diazopyridinium salts but faster than that of benzene diazonium salts (561 i. The bis-diazonium salt of bis(2-amino-4-methylthiazole) couples with /3-naphthol to give 333 (Scheme 189) (612). The products obtained from the diazo coupling are usuallv highly colored (234. 338. 339. 613-616). 

Ref 2), 184-5° (decomp) (Ref 3). Was prepd by nitrating 2-amino-4-methylthiazole with mixed nitric-sulfuric acids, as indicated in Ref 3... 

Suspend 76 g (1 mol) of thiourea (CAUTION see Section 2.3.4, p. 50) in 200 ml of water in a 500-ml three-necked flask sited in a fume cupboard and equipped with a sealed stirrer unit, a reflux condenser and a dropping funnel. Stir and add 92.5 g (80 ml, 1 mol) of chloroacetone (1) over a period of 30 minutes. The thiourea dissolves as the reaction proceeds and the temperature rises. Reflux the yellow solution for 2 hours. To the cold solution immersed in an ice bath add, with stirring, 200 g of solid sodium hydroxide. Transfer to a separatory funnel, add a little ice-water, separate the upper oil layer and extract the aqueous layer with three 100 ml portions of ether. Dry the combined oil and ether extracts with anhydrous sodium sulphate, remove the ether using a rotary evaporator and distil the residual oil under diminished pressure. Collect the 2-amino-4-methylthiazole at 130-133 °C/18mmHg it solidifies on cooling in ice to a solid, m.p. 44-45 °C. The yield is 84 g (74%). 

Infrared absorption properties of 2-aminothiazole were reported with those of 52 other thiazoles (113). N-Deuterated 2-aminothiazole and 2-amino-4-methylthiazole were submitted to intensive infrared investigations. All the assignments were performed using gas-phase studies of the shape of the vibration-rotation bands, dichroism. isotopic substitution, and separation of frequencies related to H-bonded and free species (115). With its ten atoms, this compound has 24 fundamental vibrations 18 for the skeleton and 6 for NH2. For the skeleton (Cs symmetry) 13 in-plane vibrations of A symmetry (2vc H, 2SC H. 1 vc N, 1SC N. and 7ft)nuc,eus) and five out-of-plane vibrations of A" symmetry (2yc H. 2rnilde ,. l-yc N) were assigned (Table VI-3). 

Under appropriate conditions activated thiazoles are alkylated at the 5-position 2-amino 4-methylthiazole is alkylated in the 5-position by heating with /-butyl alcohol in sulfuric acid (24). Under similar conditions 4-methyl-2-phenylthiazole is alkylated by cyclohexanol. 2-Acetylamino-4-methylthiazole reacts with dimethylamine and formaldehyde to afford the corresponding Mannich base (25). 2-Hydroxy-4-methyIthiazole fails to react when submitted to Friedel-Crafts benzoylation conditions whereas it reacts normally in Gatter-mann and in Reimer-Tiemann formylation reactions yielding the 5-formyl derivative (26). 2,4-Dimethylthiazole undergoes perfluoroalkylation when heated at 200 °C for 8 h in a sealed tube with perfluoropropyl iodide and sodium acetate (27). 

This nucleophilic reactivity of 2-aminothiazoles has been used to prepare biheterocyclic compounds. Thus 2-aminothiazole reacts with chlorovinyl methyl ketone yielding 5-methyl-thiazolo[3,2-a]pyrimidinium chloride (Scheme 109). In the presence of formaldehyde, aminothiazoles react with ends affording condensation products, through the intermediacy of Mannich bases (Scheme 110). In acidic medium and at higher temperatures, condensation of 4-aryl-2-aminothiazole with benzaldehyde takes place at the C-5 position (Scheme 111). The same orientation is observed when 2-amino-4-methylthiazole is alkylated by secondary or tertiary alcohols in 85% sulfuric acid (Scheme 112). 

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