Acyl halides derivatives

Acyl halides, both aliphatic and aromatic, react with the sodium derivative, but the product depends largely on the solvent used. Thus acetyl chloride reacts with the sodium derivative (E) suspended in ether to give mainly the C-derivative (t) and in pyridine solution to give chiefly the O-derivative (2). These isomeric compounds can be readily distinguished, because the C-derivative (1) can still by enolisation act as a weak acid and is therefore... 

After acyl halides acid anhydrides are the most reactive carboxylic acid derivatives Three of them acetic anhydride phthahc anhydride and maleic anhydride are mdus trial chemicals and are encountered far more often than others Phthahc anhydride and maleic anhydride have their anhydride function incorporated into a nng and are referred to as cyclic anhydrides... 

Carboxylic acid hydiazides are prepared from aqueous hydrazine and tfie carboxylic acid, ester, amide, anhydride, or halide. The reaction usually goes poody with the free acid. Esters are generally satisfactory. Acyl halides are particularly reactive, even at room temperature, and form the diacyl derivatives (22), which easily undergo thermal dehydration to 1,3,4-oxadiazoles (23). Diesters give dihydtazides (24) and polyesters such as polyacrylates yield a polyhydrazide (25). The chemistry of carboxyhc hydrazides has been reviewed (83,84). 

Azoles containing a free NH group react comparatively readily with acyl halides. N-Acyl-pyrazoles, -imidazoles, etc. can be prepared by reaction sequences of either type (66) -> (67) or type (70)->(71) or (72). Such reactions have been carried out with benzoyl halides, sulfonyl halides, isocyanates, isothiocyanates and chloroformates. Reactions occur under Schotten-Baumann conditions or in inert solvents. When two isomeric products could result, only the thermodynamically stable one is usually obtained because the acylation reactions are reversible and the products interconvert readily. Thus benzotriazole forms 1-acyl derivatives (99) which preserve the Kekule resonance of the benzene ring and are therefore more stable than the isomeric 2-acyl derivatives. Acylation of pyrazoles also usually gives the more stable isomer as the sole product (66AHCi6)347). The imidazole-catalyzed hydrolysis of esters can be classified as an electrophilic attack on the multiply bonded imidazole nitrogen. 

Triazoles are acylated with acyl halides, usually initially at the 1-position, but the acyl group may migrate to the 2-position on heating or on treatment with base. Thus acetylation with acetyl chloride often gives 1-acetyl derivatives, which rearrange to the 2-isomers above 120 °C (74AHCil6)33). 

The salts of the thiol react with alkyl and acyl halides to form alkyl or acyl derivatives (Table II). For a discussion of the constitution of these compounds see Section IV, D. 

The formulated mechanism is supported by the finding that no halogen from the phosphorus trihalide is transferred to the a-carbon of the carboxylic acid. For instance, the reaction of a carboxylic acid with phosphorus tribromide and chlorine yields exclusively an a-chlorinated carboxylic acid. In addition, carboxylic acid derivatives that enolize easily—e.g. acyl halides and anhydrides—do react without a catalyst present. 

Brown and Jensen395 suggested that the rate equation (194) for the reaction of benzene with excess benzoyl chloride could be interpreted according to the mechanisms given by the reactions (201) and (202), (203) and (204) and (205) and (206) which refer to nucleophilic attack of the aromatic upon the polarised acyl halide-catalyst complex, upon the free acylium ion, and upon an ion pair derived from the acyl halide-catalyst complex, viz. 

In the course of this study, the authors determined /Lvalues for dibenzyl, methyl phenyl, methyl p-nitrophenyl, di-p-tolyl, di-isopropyl and tetramethylene sulphoxides and for diethyl, dipropyl and dibutyl sulphites. The /Lscales are applied to the various reactions or the spectral measurements. The /Lscales have been divided into either family-dependent (FD) types, which means two or more compounds can share the same /Lscale, family-independent (FI) types. Consequently, a variety of /Lscales are now available for various families of the bases, including 29 aldehydes and ketones, 17 carboxylic amides and ureas, 14 carboxylic acids esters, 4 acyl halides, 5 nitriles, 10 ethers, 16 phosphine oxides, 12 sulphinyl compounds, 15 pyridines and pyrimidines, 16 sp3 hybridized amines and 10 alcohols. The enthalpies of formation of the hydrogen bond of 4-fluorophenol with both sulphoxides and phosphine oxides and related derivatives fit the empirical equation 18, where the standard deviation is y = 0.983. Several averaged scales are shown in Table 1588. 

Derivatives of these acids formed by change in the carboxy group (salts, esters, lactones, acyl halides, amides, nitriles, etc.) are named according to 2-Carb-20.2. The anion takes the ending -uronate . Esters are also named using the ending -uronate . 

This chapter covers not only nuclear and extranuclear quinoxahnecarboxylic acids (and anhydrides) but also the carboxylic esters, acyl halides, carboxamides, carbohydrazides, carbonitriles, carbaldehydes, and (ketonic) acyl derivatives of quinoxaline a few related speceis are also included. To avoid repetition, the interconversions of these quinoxaline derivatives are discussed only at the first opportunity thus the esterification of quinoxalinecarboxylic acids in covered as a reaction of carboxylic acids rather than as a preparative route to carboxylic esters, simply because the section on carboxylic acids precedes that on carboxylic esters. To minimize any confusion, appropriate cross-references have been inserted. 

Tertiary alkyl azides can be prepared by stirring tertiary alkyl chlorides with NaN3 and ZnCl2 in 82 ° or by treating tertiary alcohols with NaN3 and CF3-COOH or with HN3 andTiCl4 or BF3. Acyl azides, which can be used in the Curtius reaction (18-14), can be similarly prepared from acyl halides, anhydrides, " esters, or other acyl derivatives. ° Acyl azides can also be prepared... 

Formation of Acyl Halides from Acid Derivatives... 

Other carbanionic groups, such as acetylide ions, and ions derived from a-methylpyridines have also been used as nucleophiles. A particularly useful nucleophile is the methylsulfinyl carbanion (CH3SOCHJ), the conjugate base of DMSO, since the P-keto sulfoxide produced can easily be reduced to a methyl ketone (p. 549). The methylsulfonyl carbanion (CH3SO2CH2 ), the conjugate base of dimethyl sulfone, behaves similarly, and the product can be similarly reduced. Certain carboxylic esters, acyl halides, and DMF acylate 1,3-dithianes (see 10-10. )2008 Qxj(jatjye hydrolysis with NBS or NCS, a-keto aldehydes or a-... 

For lists of reagents converting acid derivatives to acyl halides, see Ref. 568, pp. 977,980, 985. 

A number of other methods exist for the a halogenation of carboxylic acids or their derivatives. Acyl halides can be a brominated or chlorinated by use of NBS or NCS and HBr or HCl. The latter is an ionic, not a free-radical halogenation (see 14-2). Direct iodination of carboxylic acids has been achieved with I2—Cu acetate in HOAc. " ° Acyl chlorides can be a iodinated with I2 and a trace of HI. Carboxylic esters can be a halogenated by conversion to their enolate ions with lithium A-isopropylcyclohexylamide in THF and treatment of this solution at -78°C with... 

Allylic silanes react with aldehydes, in the presence of Lewis acids, to give an allyl-substituted alcohol. In the case of benzylic silanes, this addition reaction has been induced with Mg(C104)2 under photochemical conditions. The addition of chiral additives leads to the alcohol with good asymmetric induction. In a related reaction, allylic silanes react with acyl halides to produce the corresponding carbonyl derivative. The reaction of phenyl chloroformate, trimethylallylsilane, and AICI3, for example, gave phenyl but-3-enoate. ... 

Reaction between acyl halides and organometallic compounds 10-115 Reaction between other acid derivatives and organometallic compounds... 

In addition to acyl halides and acid anhydrides, there are a number of milder and more selective acylating agents that can be readily prepared from carboxylic acids. Imidazolides, the (V-acyl derivatives of imidazole, are examples.115 Imidazolides are isolable substances and can be prepared directly from the carboxylic acid by reaction with carbonyldiimidazole. 

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