Pyridines derivs

Hantzsch synthesis The formation of pyridine derivatives by the condensation of ethyl acetoacetate with ammonia and an aldehyde. Also applied to similar syntheses of pyrroles. 

This reaction consists of the condensation of two molecular equivalents of a 1,3 diketone (or a J3-keto-ester) with one equivalent of an aldehyde and one of ammonia. Thus the interaction of ethyl acetoacetate and acetaldehyde and ammonia affords the 1,4-dihy dro-pyridine derivative (1), which when boiled with dilute nitric acid readily undergoes dehydrogenation and aromatisation" to gb e the diethyl ester of collidine (or 2,4,6-trimethyl-pyridine-3,5 dicarboxylic acid (II)). For the initial condensation the solid aldehyde-ammonia can conveniently be used in place of the separate reagents. 

The high reactivity of the exocyclic 4-NH- group is again illustrated by the reaction of 2-imino-3-phenyl-4-amino-5-(ethoxycarbonyl)-4-thiazoline with EtOjCCH SCN, which yields 134 (296), and by the intramolecular preparation of the dihydrothiazolo[4,5-h]pyridine derivative 136 (297) (Scheme 89). 

The stereo aspect of the condensation has been studied for pyridine derivatives, and according to the nature of solvent, either ethanol or acetic anhydride, a cis or a tmns dye could be obtained (59). 

Alkylselenazoles are oily alkaline liquids possessing a smell similar to that of the corresponding thiazole or pyridine derivatives. The crystalline picrates or 3-methylselenazolium iodides have been used for the purpose of characterization. Alkyl derivatives are partially soluble in water aryl derivatives are insoluble. 

See also Isomcotimc hydrazide.) [PYRIDINE AND PYRIDINE DERIVATIVES] (Vol 20)... 

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethyl amine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcohoHc solution of ammonia and the mixture is heated to 50—75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated siHca—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH2CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

Figure 3 shows the production of acetaldehyde in the years 1969 through 1987 as well as an estimate of 1989—1995 production. The year 1969 was a peak year for acetaldehyde with a reported production of 748,000 t. Acetaldehyde production is linked with the demand for acetic acid, acetic anhydride, cellulose acetate, vinyl acetate resins, acetate esters, pentaerythritol, synthetic pyridine derivatives, terephthaHc acid, and peracetic acid. In 1976 acetic acid production represented 60% of the acetaldehyde demand. That demand has diminished as a result of the rising cost of ethylene as feedstock and methanol carbonylation as the preferred route to acetic acid (qv). 

The nameplate capacities for acetaldehyde production for the United States in 1989 are shown in Table 5 (120). Synthetic pyridine derivatives, peracetic acid, acetate esters by the Tischenko route, and pentaerythritol account for 40% of acetaldehyde demand. This sector may show strong growth in some products but all of these materials maybe prepared from alternative processes. 

Attempts to broaden the range of materials available as dye precursors have been made (34,35). Oxidative dyes based on pyridine derivatives produce less sensitization than those based on benzene derivatives (36) however, they lack tinctorial power, lightfastness, and availabihty. Derivatives of tetra am in opyrim i din e are claimed to act as primary intermediates to give intense shades with good fastness and excellent toxicological properties (37). 

Detoxifica.tlon. Detoxification systems in the human body often involve reactions that utilize sulfur-containing compounds. For example, reactions in which sulfate esters of potentially toxic compounds are formed, rendering these less toxic or nontoxic, are common as are acetylation reactions involving acetyl—SCoA (45). Another important compound is. Vadenosylmethionine [29908-03-0] (SAM), the active form of methionine. SAM acts as a methylating agent, eg, in detoxification reactions such as the methylation of pyridine derivatives, and in the formation of choline (qv), creatine [60-27-5] carnitine [461-06-3] and epinephrine [329-65-7] (50). 

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