Primary amines carbamate

Willis has similarly noted that indoles can be prepared via the cascade coupling of the aryl-halide and vinyl-triflate bonds in styrene 21 with primary amines (Scheme 6.41). Despite the fact that two different types of C—X bonds must be activated, this process proceeds with a single palladium catalyst (Pd2dba3/Xantphos), and a range of primary amines, carbamates and amides. More recently, even vinyl chlorides were found to participate in this coupling reaction [53]. 

Industrially, polyurethane flexible foam manufacturers combine a version of the carbamate-forming reaction and the amine—isocyanate reaction to provide both density reduction and elastic modulus increases. The overall scheme involves the reaction of one mole of water with one mole of isocyanate to produce a carbamic acid intermediate. The carbamic acid intermediate spontaneously loses carbon dioxide to yield a primary amine which reacts with a second mole of isocyanate to yield a substituted urea. 

There is an industry trend to supply SBR certifiably free of volatile nitrosamines or nitrosatable compounds. This has generally been accomplished by replacing shortstop systems based on carbamates and hydroxyl amines with products that are not based on secondary amines or are secondary amines of high molecular weight, such as dibenzyldithiocarbamate. A more recendy issued patent for ESBR shortstop is based on isopropyUiydroxylamine, a primary amine that does not form nitrosamine (46). 

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 conversion of the BOC group to other carbamates is achieved by heating the alcohol, Ti(0-/-Pr)4 in toluene. Teoc-, Cbz-, and Alloc-pro-tected primary amines have been prepared in this fashion. The reaction is selective for a primary BOC derivative. ... 

After activation with peracetic acid and base treatment, derivatives of primary amines form the isocyanate, which can be trapped with water to effect hydrolysis or with an alcohol to form other carbamates. 

Our recent studies on effective bromination and oxidation using benzyltrimethylammonium tribromide (BTMA Br3), stable solid, are described. Those involve electrophilic bromination of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophene, a-bromination of arenes and acetophenones, and also bromo-addition to alkenes by the use of BTMA Br3. Furthermore, oxidation of alcohols, ethers, 1,4-benzenediols, hindered phenols, primary amines, hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are also presented. 

Oxidative carbonylation generates a number of important compounds and materials such as ureas, carbamates, 2-oxazolidinones, and aromatic polycarbonates. The [CuX(IPr)] complexes 38-X (X = Cl, Br, I) were tested as catalysts for the oxidative carbonylation of amino alcohols by Xia and co-workers [43]. Complex 38-1 is the first catalyst to selectively prepare ureas, carbamates, and 2-oxazolidinones without any additives. The important findings were the identity of the counterion and that the presence of the NHC ligand influenced the conversions. 2-Oxazohdinones were formed from primary amino alcohols in 86-96% yield. Complex 38-1 also catalysed the oxidative carbonylation of primary amines to ureas and carbamates. n-Propylamine, n-butylamine, and t-butylamine were transformed into the... 

Carbamates by Reaction with Carbamoylazoles (AzoIe-TV-Carboxamides) of Primary Amines... 

Absorbents based on a variety of amines are by far the most common. Amines that have been used include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diisopropanolamine (DIPA), methyl diethanolamine (MDEA), and digly-colamine (DGA). C02 is typically absorbed at 80-140°F temperature and up to 1000 psig pressure by chemically reacting with the basic amine functional group in the absorbent, for example, primary amine, MEA, reacts with C02 by the following reaction forming a carbamate salt ... 

All amines are relatively weak bases, which react with C02, H2S, and COS forming bonds that can easily be broken at elevated temperatures. Primary amines are chemically stronger than secondary, which in turn are stronger than tertiary. Weaker amines have greater selectivity for H2S, which is especially high for tertiary amines where the nitrogen atom does not have a free hydrogen association to form the carbamate ion by direct reaction... 

The procedure has been extended to the synthesis of 7V,7V -substituted diamines 166 from the diazides 164 and dichloroboranes 165177. Primary amines protected by the t-butoxycarbonyl group are obtained by the action of trialkylboranes R3B (R = Bu, s-Bu, CsHn or cyclohexyl) on the lithium or potassium salt of t-butyl 7V-(tosyloxy)carbamate (equation 62)178. 

Acetoxymethyl carbamates of primary amines behaved differently from the pathway depicted in Fig. 8.19, the predominant reaction being intramolecular acyl transfer to generate the A-acetylated amine as the major product [209]. This parasitic reaction was observed in buffer and proportionally less in plasma, disqualifying (acyloxy)methyl carbamates for use as prodrugs of primary amines. However, this type of derivative appears well suited for the preparation of prodrugs of secondary amines, as documented below. 

Fig. 11.11. Mechanism postulated for hydrolysis of organic isocyanates involving electrophilic addition of H20 with general base catalysis. The product of hydration is a carbamic acid that spontaneously decomposes to the primary amine with loss of C02 [117].

The carbamation of primary amines with DMC is a known process, though only catalyzed reactions proceed with good yields and selectivity (Scheme 4.20). ... 

The instability of primary nitramines in acidic solution means that the nitration of the parent amine with nitric acid or its mixtures is not a feasible route to these compounds. The hydrolysis of secondary nitramides is probably the single most important route to primary nitramines. Accordingly, primary nitramines are often prepared by an indirect four step route (1) acylation of a primary amine to an amide, (2) A-nitration to a secondary nitramide, (3) hydrolysis or ammonolysis with aqueous base and (4) subsequent acidification to release the free nitramine (Equation 5.17). Substrates used in these reactions include sulfonamides, carbamates (urethanes), ureas and carboxylic acid amides like acetamides and formamides etc. The nitration of amides and related compounds has been discussed in Section 5.5. 

Ionic liquids have been used for the selenium- or palladium-catalyzed carbonylation of primary amines to form carbamates or ureas.After completion of the carbonylation, addition of water induced the precipitation of desired products, which were isolated by fdtration and separated from the ionic liquid, containing the catalytic species. Then, the catalyst could be reused after removal of residual methanol and water by distillation. Although the conversion of the reaction slightly decreased after the second run, the catalytic activity was considerably improved (from 70% to 99 %) by the addition of a small amount of the fresh catalyst. " ... 

Thus, reaction of tetrahydrofuroic acid (40-1) with triphenylphosphoryl azide leads to isocyanate (40-2). Treatment of this intermediate with benzyl alcohol then affords the corresponding carbamate (40-3). Catalytic hydrogenation removes the benzyloxy group, leading to the free primary amine. That product is then resolved by way of its camphorsulfonyl salt to afford (40-5). Reaction of this intermediate with desamino chloroadenosine (40-6) affords tecadenoson (40-7) [42]. 

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