Amino groups, reactivities

TFDB strongly affects the reduction of amino group reactivity by introducing. -CF3 in the meta (m-) position. The polymerization reactivity of diamines and... 

The diazotization of 5-aminotetrazole as a general preparative method for 5-substituted tetrazoles with versatile simple substituents is still important. For instance, the preparation of N-unsubstituted 5-nitrotetrazole 397 through 5-nitrotetrazole sodium salt tetrahydrate <1997RJ01771> is a significant achievement of the last decade and demonstrates new features of the amino group reactivity in 5-aminotetrazole derivatives (Scheme 46). 

The amino group of 2-imino-3-phenyl-4-amino-5-carbethoxy-A4-thiazoline is very reactive and displaces the chlorine atom of various 2-chlorothiazoles (1577). 

The amino group is expected to have decreased reactivity in thiazolium salts. 2-Amino-4,5-trimethylene thiazole (224) heated in diluted HQ at 80°C, however, gives the product 227a (463). The probable mechanism is shown in Scheme 139. This mechanism suggests a retro-Hantzsch ... 

The terminal amino group of 2-hydrazino-4-phenylthiazole is also the reactive center in reactions with activated aryl halides such as 288. A solution of the product (289) obtained from this reaction when shaken with PbOj gives a deeply colored radical, whose structure has been studied by ESR (Scheme 173) (532. 533). 

Regarding the substituent effect on reactivity of groups in positions 4 and 5 there is little information in the literature. The reactivity of halogen in position 5 seems to be increased when an amino group is present in position 2. Substitution products are easily obtained using neutral nucleophiles such as thiourea, thiophenols, and mercaptans (52-59). 

Protecting the amino group of an arylamine in this way moderates its reactivity and per mits nitration of the ring to be achieved The acetamido group is activating toward elec trophilic aromatic substitution and is ortho para directing... 

Fiber-reactive dyes containing the fluorotriaziayl group are based on the condensation of chromophores containing amino groups with 6 - sub s titute d- 2,4- diflu o r o triaziae s. The latter can be prepared from cyanuric fluoride or from the reaction of alkah metal fluorides with... 

Monomer Reactivity. The poly(amic acid) groups are formed by nucleophilic substitution by an amino group at a carbonyl carbon of an anhydride group. Therefore, the electrophilicity of the dianhydride is expected to be one of the most important parameters used to determine the reaction rate. There is a close relationship between the reaction rates and the electron affinities, of dianhydrides (12). These were independendy deterrnined by polarography. Stmctures and electron affinities of various dianhydrides are shown in Table 1. 

The aminophenols are chemically reactive, undergoing reactions involving both the aromatic amino group and the phenoHc hydroxyl moiety, as weU as substitution on the benzene ring. Oxidation leads to the formation of highly colored polymeric quinoid stmctures. 2-Aminophenol undergoes a variety of cyclization reactions. 

Aminophenols. Reaction of chloroformate with aminophenols (qv) also takes place at the more reactive amino group selectively. Thus (9-aminophenol [95-55-6] gives benzoxazolone [59-49-4] by cyclization of the intermediate carbamate (31). 

Amino Acids. Chloroformates play a most important role for the protection of the amino group of amino acids (qv) during peptide synthesis (32). The protective carbamate formed by the reaction of benzyl chloroformate and amino acid (33) can be cleaved by hydrogenolysis to free the amine after the carboxyl group has reacted further. The selectivity of the amino groups toward chloroformates results in amino-protected amino acids with the other reactive groups unprotected (34,35). Methods for the preparation of protected amino acids on an industrial scale have been developed (36,37). A wide variety of chloroformates have been used that give various carbamates that are stable or cleaved under different conditions. 

The amino group in cyanamide is very reactive toward formaldehyde. The reaction produces first an unstable hydroxymethyl derivative that... 

In 1956, ICI commercia1i2ed the first dyes promoted as reactive dyes for cotton. These dyes were marketed under the trade name Procion and contained the dichlorotria2ine reactive group bridged to dye through an amino group. 

The reactivity of the amino groups at the pteridine nucleus depends very much upon their position. All amino groups form part of amidine or guanidine systems and therefore do not behave like benzenoid amino functions which can usually be diazotized. The 4-, 6-and 7-amino groups are in general subject to hydrolysis by acid and alkali, whereas the 2-amino group is more stable under these conditions but is often more susceptible to removal by nitrous acid. 

Substituents in the indazole ring may direct a given reaction towards another position either by their R and I electronic properties or simply by protecting the most reactive position. Examples of both types are found in sulfonation studies (67HC(22)l). As indicated before (Section 4.04.2.3.2(i)), sulfonation takes place at position 7. However, the presence of an amino group at positions 5 or 7 directs the attack towards the 4-position (Scheme 40). To obtain the indazole-5-sulfonic acid a more complicated procedure has been used but it is still based on the same ideas. 

When the 1-position is substituted, 3- and 5-aminopyrazoles react at the C-4 carbon atom, the reactivity of which is enhanced by the amino group. Thus pyrazolo[3,4-Z ]pyridines (545) are obtained either by the Skraup synthesis or from 1,3-diifunctional compounds. Here also aminopyrazolinones have been used instead of aminopyrazoles to prepare (545 R = OH). If 1,4-ketoesters (succinic acid derivatives) are used instead of /3-ketoesters, pyrazolo[3,4-Z ]azepinones (546) are obtained. 

Reactivity Chart 8. Protection for the Amino Group Carbamates... 

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