Halides heterocyclic bases

The common impurities found in amines are nitro compounds (if prepared by reduction), the corresponding halides (if prepared from them) and the corresponding carbamate salts. Amines are dissolved in aqueous acid, the pH of the solution being at least three units below the pKg value of the base to ensure almost complete formation of the cation. They are extracted with diethyl ether to remove neutral impurities and to decompose the carbamate salts. The solution is then made strongly alkaline and the amines that separate are extracted into a suitable solvent (ether or toluene) or steam distilled. The latter process removes coloured impurities. Note that chloroform cannot be used as a solvent for primary amines because, in the presence of alkali, poisonous carbylamines (isocyanides) are formed. However, chloroform is a useful solvent for the extraction of heterocyclic bases. In this case it has the added advantage that while the extract is being freed from the chloroform most of the moisture is removed with the solvent. 

The /3-d configuration was assigned40 to 82 on the basis of the trans rule,83 as exemplified by the reaction of glycosyl halides with heavy-metal salts of heterocyclic bases.833 Unambiguous chemical proof was secured from the transformation of the nitrile into the corresponding acid (21). 

Azalene salts 90 and 92 are obtained by quaternization of the corresponding heterocyclic bases with alkyl halides or tosylates. If the heterocyclic base contains several nitrogen atoms, alkylation can produce different quaternary salts. Quaternization, however, is surprisingly selective if certain conditions are met.205 Pyrrolo- and indolopyridines containing one pyridine-and one pyrrole-type nitrogen atom in their molecular lattice are (in aprotic solvents) almost exclusively alkylated at the nitrogen atom of the pyridine... 

If the heterocyclic base contains several pyridine-type nitrogens select can also be observed. Indeno[l,2-b]quinoxalines, for example, are quaternized at the N-10 atom.110 The alkylation of heterocycles conta one pyrrole-type nitrogen and several pyridine-type nitrogens is appar selective (e.g., indolo[2,3-b]quinoxaline).201 The yields of quaternary however, are extremely low,201 even if phenacyl halides or a-halo ester used.207 Perhaps the resultant quaternary salts are dealkylated.200,207... 

Quaternary salts (90) from azalenes obtained from heterocyclic bases and phenacyl halides or derivatives of a-halo carbon acids also contain an acidic exocyclic CH2 group. Therefore, during the deprotonation, mixtures of pseudoazulenes 91 and ylides 98 can be formed, especially if Y = CH. °5 Quaternary salts (90) containing one pyrrole-type nitrogen (Y = N) de-protonate exclusively to pseudoazulenes166 (Scheme 6). Analogous behavior... 

In the presence of alkyl halides and base, alkyltetracarbonylcobalt complexes are formed with Co2(CO)8 these species [RCo(CO)4] carbonylate a wide range of aryl halides or heterocyclic halides to various products, which depend upon the specific conditions. In the presence of alcohols, carboxylic esters are formed. Under phase transfer conditions and with iodomethane, mixtures of methyl ketone and carboxylic acid formation are realized (equation 207). In the presence of sodium sulfide or NaBH4 in water-Ca(OH)2 (equation 208) good amounts of double carbonylation are realized under very mild conditions412-414. 

Ring transformation of 2-amino-3-phenacyl-l,3,4-oxadiazolium halides with amines, liquid ammonia, or heterocyclic bases yields 2-amino-l-acylamino-4-arylimidazoles.145... 

An extremely convenient and general " " method of Reissert compound formation has been developed. This involves the addition of the acid halide (or less frequently anhydride) neat or in methylene chloride to a mixture of the heterocyclic base in methylene chloride and potassium cyanide in a minimum of water. Although the methylene chloride-water system is heterogeneous it has the advantage over the aqueous system that all the reactants and products are soluble in one phase or the other. Also water is slightly soluble in methylene chloride. The amount of water present is not sufficient to prevent the use of even reactive acid chlorides. This system appears to be the method of choice for Reissert compound formation. 

Ring transformation of 2-amino-3-phenacyl-l,3,4-oxadiazolium halides with amines, liquid ammonia or heterocyclic bases gives l-acylamino-2-amino-4-arylimidazoles [57], When treated with an a-halogenoketone in ethanol 2,5-diamino-1,3,4-thiadiazolcs form salts, which react with hydrazine hydrate to give l-aminoimidazolin-2-thiones [58],... 

In the case of organochromium(III) complex intermediates obtained from glycosyl halides, work by Somsak and coworkers showed that their decay into glycals [75] is marked by the remarkable stability of the organometalic compounds in aqueous solutions. From the same group came the radically new concept of using zinc metal under aprotic conditions [76]. In brief, they proposed that acetylated glycosyl bromides be treated with zinc dust in the presence of A-heterocyclic bases (e. g., 4-methylpyridine or 1-methylimidazole) in a variety of aprotic solvents (i. e., benzene, ethyl acetate, tetrahydrofuran, acetone, dichloromethane) to afford the... 

In the benzoin condensation, one molecule of aldehyde serves as an electrophile. If a carbanion is generated from protected cyanohydrins, a-aminonitriles or dithioacetals, it can react with electrophiles such as alkyl halides, strongly activated aryl halides or alkyl tosylates to form ketones. Amongst other electrophiles which are attacked by the above carbanions are heterocyclic A -oxides, carbonyl compounds, a,p-unsaturated carbonyl compounds, a,3-unsaturated nitriles, acyl halides, Mannich bases, epoxides and chlorotiimethyl derivatives of silicon, germanium and tin. 

Pyndo 3,4-6]pyrazine, as well as its 2-phenyl and 2,3-diphenyl derivative, give mono-Reis-sert compounds and analogs by treatment with an equivalent amount each of the heterocyclic base, trimethylsilyl cyanide, acyl halide, or ethyl chloroformate, and a catalytic amount of aluminum trichloride.113... 

Halide salts of quaternary ammonium and phosphonium cations, and those derived from heterocyclic bases (both aromatic and alicyclic), have long been known (Table 11.14). Most are relatively high melting (and would not be considered ionic liquids), though the structural characteristics of quaternary ammonium halides have been studied by those with interests in plastic crystals and so-called rotator phases [7]. Many deconpose at or near their melting temperatures, a characteristic that would limit interest in them as reaction media [667]. Indeed, it is probably as a result of the view, widely held in the past [668], that such materials may be intrinsically unstable that the onset of the recent massive interest in ionic liquids was delayed. 

A wide class of aiyl-based quaternary surfactants derives from heterocycles such as pyridine and quinoline. The Aralkyl pyridinium halides are easily synthesized from alkyl halides, and the paraquat family, based upon the 4, 4 -bipyridine species, provides many interesting surface active species widely studied in electron donor-acceptor processes. Cationic surfactants are not particularly useful as cleansing agents, but they play a widespread role as charge control (antistatic) agents in detergency and in many coating and thin film related products. 

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