Thiazoles imino

Macroreticular polystyrene-based resins with functional aminothiazole, imino-thiazole, or thiazoline groups exhibit a high selectivity for mercury(II). A thiazoline resin column has been used to concentrate mercury from sea water adjusted to pH 1 with hydrochloric acid. Maximum sorption capacity for mercury was found to be 2.8 mmole/g. The sorbed mercury is recovered quantitatively by eluting with 0.1 M HC1 containing 5 % thiourea 100). 

The product with m.p. 83,5—84.5° C which Jacobson isolated appears to have been 3,4,4-trialkyl thiazolidin-5-one-2-thione rather than l,5,5-trimethylimidazolidine-2,4-dithione. The former can be synthesized independently from a-(methylamino) isobutyric acid and carbon disulfide (see also V.3). Other a-(methylamino) nitriles when refluxed with carbon disulfide, also yield 3,4,4-trialkyl-5-imino thiazol-idine-2-thiones (CLXII) (listed in Table 23) which can be hydrolyzed... 

The thiadiazine (428) (see p. 211) undergoes a quantitative rearrangement to the tri-imino-thiazole (429) upon treatment with base. ° Thermal extrusion of NH from the benzo[e]-l,2,4-thiadiazine (430) is far more difficult than from the analogous oxadiazine, which loses NH upon refluxing in benzene. The reaction can, however, be performed at room temperature by the use of triphenylphosphine, which forms a complex with (430) this complex is converted into the thiazole (431) (98%) and triphenylphosphine oxide upon elution through silica (Scheme 166). 

Physicochemical studies on aminothiazoles are mainly centered on two problems the position of imino-amino protomeric equilibrium and IsRR substitution effects on the thiazole nucleus. 

Charge diagrams for 2-aminothiazole and 2-imino-4-thiazoline, calculated using HMO. PPP, and CNDO approximations, are illustrated in Fig. VI-1. When compared to Table 1-2 for thiazole itself it appears that the... 

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),... 

Most of the spectroscopic properties of 2-imino-4-thiazolines have been treated in Section II. Paper chromatography and thin-layer chromatography are particularly suitable for distinguishing 2-atnino-thiazoles from 2-imino-4-thiazolines their RfS and characteristic reactions are different (148, 494. 705). 

Nucleophilic reactivity of the sulfur atom has received most attention. When neutral or very acidic medium is used, the nucleophilic reactivity occurs through the exocyclic sulfur atom. Kinetic studies (110) measure this nucleophilicity- towards methyl iodide for various 3-methyl-A-4-thiazoline-2-thiones. Rate constants are 200 times greater for these compounds than for the isomeric 2-(methylthio)thiazole. Thus 3-(2-pyridyl)-A-4-thiazoline-2-thione reacts at sulfur with methyl iodide (111). Methyl substitution on the ring doubles the rate constant. This high reactivity at sulfur means that, even when an amino (112, 113) or imino group (114) occupies the 5-position of the ring, alkylation takes place on sulfiu. For the same reason, 2-acetonyi derivatives are sometimes observed as by-products in the heterocyclization reaction of dithiocarba-mates with a-haloketones (115, 116). 

The controversy seemed then to be closed. In 1890 Hantzsch had already started his work on the structure of oximes, and his synthetic work on heterocycles was practically ended. However, 27 years later, in July 1919, Tcherniac published a new paper entitled TTiiocyanoacetone and its derivatives as isomerides (33), where, after the description of improved and generalized methods for the preparation of thiocyanoacetone he came to the explosive conclusion that the substance which has been known since 1887 as hydroxymethylthiazole is not a thiazole at all. It might be called 2-imino-4-methylthioxole, but for the sake of simplicity, and in view of the now proved existence of two other isomerides of thiocyanoacetone, it seems preferable to adopt the generic... 

Of all the methods described for the synthesis of thiazole compounds, the most efficient involves the condensation of equimolar parts of thiourea (103) and a-haloketones or aldehydes to yield the corresponding 2-aminothiazoles (104a) or their 2-imino-A-4-thiazoline tautomers (104b) with no by-products (Method A, Scheme 46). 

The symmetrical disubstituted thioureas such as 137 do not give a thiazolic ring (Scheme 66), but give compounds of type 138 or 139, which are derived from the tautomer imino form of the 2-aminothiazole (86). 

Thiazole, 2-acetylamino-4-methyl-alkylation, 6, 256 Thiazole, 2-acylamino-4-hydroxy-synthesis, 6, 297 Thiazole, 5-alkoxy-cleavage, 6, 289 synthesis, 6, 302 Thiazole, 2-alkyl-A7-alkylation, 6, 253 hydrogen exchange, 6, 276 methylation, 6, 253 quatemization, 6, 253-254 reactions, S, 88 Thiazole, 4-alkyl-A7-alkylation, 6, 253 methylation, 6, 253 quatemization, 6, 253-254 Thiazole, 5-alkyl-A7-alkylation, 6, 253 methylation, 6, 253 Thiazole, 2-alkylamino-tautomerism, 6, 248 Thiazole, 4-alkyl-2,5-dimethyl-quatemization, 6, 253-254 Thiazole, 2-alkylthio-reactions, S, 103 rearrangement, 5, 103 6, 291 Thiazole, 3-allyl-4-hydroxy-2-imino-synthesis, 6, 297 Thiazole, 2-allyloxy-rearrangement, 6, 289 Thiazole, 2-amino-diazo coupling, 6, 257 nitration, 6, 255... 

Grignard reagents from, 5, 106 reactions, 5, 104 6, 274, 292 reactivity, 6, 292 synthesis, 6, 297 Thiazoles, imino-reactivity, 6, 250 Thiazoles, isopropenyl-radical polymerization, 6, 278 Thiazoles, mercapto-industrial uses, 6, 330 reactions, 5, 102 synthesis, 6, 298-299 tautomerism, 6, 247, 248, 269, 289 Thiazoles, methyl-... 

Sheinkcr and his co-workers have used ultraviolet and infrared spectroscopic data to show that the imino form of benzenesul-fonamido derivatives of thiazoles and l-thia-3,4-diazoIes is preferred to the amino form by a large factor. In view of this work, the formulation of 2-aryIsulfonamidooxazoles in the amino form on the basis of chemical evidence must be regarded with caution. 

Imino-1,2,4-thiadiazoles such as 27 react with electron-deficient alkynes to afford arylimino thiazoles such as 28. There has been some speculation as to the mechanism of this reaction, which may involve a 1,3-dipolar cycloaddition or a stepwise nucleophilic addition (Equation 6) <1996CHEC-II(4)307>. 

A synthesis from thiazole precursors occurred when 2-imino-3,4-diarylthiazolines (234) were cyclized with formaldehyde to give 236 [79IJC(B)632]. 

However, the dicyano ylids (216a, b) failed to give the aromatic azapentalenes 217 with DMAD. The products isolated were the imino-azapyrrocoline 218a or the fused thiazole 218b as shown in Eq. (25). 

Heating 4-azidothiazoles having an imino or aldehyde group at the 5-position affords fused pyrazolo- and isoxazolo[3,4-d]thiazoles (Equation (7)). When an alkenyl group is in 5-position of the triazole ring, 4//-pyrrolo[2,3-[Pg.454]

Thiazoles, vinyl-radical polymerization, 6, 278 Thiazole-5-sulfonic acid, 2-amino-synthesis, 6, 255-256 Thiazole-2-sulfonic acids reactions, 5, 104 6, 291 Thiazole-5-sulfonic acids synthesis, 6, 255 Thiazole-5-thione, 2-phenyl-tautomerism, 6, 249 Thiazolethiones reactivity, 6, 250 Thi azole-2-thiones reactions, 5, 102 tautomerism, 5, 367 Thiazolidine, 2-alkyl-occurrence, 6, 327 Thiazolidine, 2-arylimino-X-ray analysis, 6, 238 Thiazolidine, 4-imino-mesoionic didehydro derivative nomenclature, 1, 34 nomenclature, 1, 34... 

Addition of 5.00 g (0.0158 mole) of 3 -[l-hydroxy-2-(2-imino-3-thiazolidinyl)ethyl]acetanilide hydrochloride to 15 ml of concentrated sulfuric icid is carried out in small increments over 0.5 h. The orange solution is stirred an additional 1 h, poured onto ice and made basic with concentrated ammonium hydroxide. The aqueous base is extracted twice with chloroform and the combined organic layers washed with water, brine, dried (sodium sulfate) and evaporated at reduced pressure to give 3.32 g (80% crude yield) of the 3 -(2,3,5,6-tetrahydroimidazo[2,l-b]thiazol-6-yl)acetanilide, melting point 164-166°C (recrystallization from 2-propanol). 

Some methods are based on the enlargement of five- or four-membered heterorings. Thus, thiazole-1,1-dioxides 50 were transformed into 2-imino-TAs 51 by a reaction with carbon disulfide, methyl iodide, and potassium tm-butoxide (75GDP108991, 75ZC480) (Scheme 13). 

As mentioned earlier in Section III,C, 6, 3-amino-2,l-benziso-thiazole displays reactions which yield fixed products of the tautomeric 3-imino form. Ross has prepared a number of 3-alkylimino and 3-arylimino derivatives.103... 

Platinum complexes, 161 Polarographic studies, 153, 154 of 2-aminothiazoles, 29 of 2-anilinothiazoles, 30 of 2-azothiazoles, 107, 108 Polyacrylonitrile, 105, 163, 164, 167 Polyamines, 156-168 Polycaprolactam, 156-168 Polyesters, 163, 165, 166, 167 Polyhalogenothiazole. reactivity of, 408-409 Polymers, e-caprolactam, butadiene, 438 Polymorphism, of sulfathiazole, 116 Positive colored image, 440 Postemergence activity, 134 Potassium salts, of acetamido thiazoles, 90 Potentiometric measurements, and amido-imido equilibrium, 116 and amino-imino equilibrium, 21 P.P.P. approximation, charge diagrams calculations by, 17... 

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