Halo acid

This reaction is of synthetic value in that a halo acids are reactive sub strates m nucleophilic substitution reactions... 

Nucleophilic substitution by ammonia on a halo acids (Section 19 16) The a halo acids obtained by halogenation of car boxylic acids under conditions of the Hell-Volhard-Zelinsky reaction are reac tive substrates in nucleophilic substitu tion processes A standard method for the preparation of a ammo acids is dis placement of halide from a halo acids by nucleophilic substitution using excess aqueous ammonia... 

The a halo acid is normally prepared by the Hell-Volhard-Zehnsky reaction (see Sec tion 19 16)... 

Preparation. The general preparation of y acids is by the hydrolysis of an a-halo acid or by the acid hydrolysis of the cyanohydrins of an aldehyde or a ketone. 

Substitution Reactions. Reaction with nitrous acid in dilute aqueous solutions yields the corresponding hydroxy acid or in solution containing a hydrohahc acid, the corresponding a-halo acid, with inversion in many cases. 

Various alkylating agents are used for the preparation of pyridazinyl alkyl sulfides. Methyl and ethyl iodides, dimethyl and diethyl sulfate, a-halo acids and esters, /3-halo acids and their derivatives, a-halo ketones, benzyl halides and substituted benzyl halides and other alkyl and heteroarylmethyl halides are most commonly used for this purpose. Another method is the addition of pyridazinethiones and pyridazinethiols to unsaturated compounds, such as 2,3(4//)-dihydropyran or 2,3(4//)-dihydrothiopyran, and to compounds with activated double bonds, such as acrylonitrile, acrylates and quinones. 

The salts of -halo acids cyclize in ionizing media to oxetan-2-ones, as do -diazonium carboxylates (64HC(19-2)787). Thietanes are obtained analogously (Section... 

Bromination of the substituted butyric acid, 26, by the Hell-Volhardt-Zelinsky procedure affords the a-halo acid bromide (27). Reaction of this with urea affords directly bromisovalum (28). 

Halo Acids, Esters, Aldehydes, Ketones see Halo Carbonyl Compounds) Haloamines... 

The tosylatc must come from alcohol (44), Disconnection Lo an epoxide (45) is no good as the amine will attack the wrong atom. Change of oxidation level to (46) is more hopeful as the a-halo acid (47) is easily made. Another possibility is to use naturally occurring a 1 an ine ( 48),... 

Although alcohols are oxidized by tetra-n-butylammonium persulphate when the reaction is conducted in dichloromethane, tetrahydropyranyl ethers have been produced (>90%) when attempts to oxidize the alcohol are conducted in tetrahydro-pyran (see Chapter 10) [ 19], Tetrahydrofuranyl ethers have been prepared by an analogous method [20,21 ]. Base-mediated elimination of halo acids from P-halo alcohols under phase-transfer catalysed conditions produce oxiranes in high yield (70-85%). The reaction has particular use in the synthesis of epihalohydrins from p,y-dihalo alcohols [22],... 

An interesting C-S bond formation mediated by benzyltriethylammonium tetrathiomolybdate converts -halo acid chlorides into thiolactones [64] (Scheme 4.16). 

The second method of intramolecular cyclization to 2,5-DKPs involves formation of the Ni—Ce bond. This reaction entails acylation of glycinamide with an a-halo acid halide, followed by ring closure under basic conditions. ... 

In aqueous acid solutions, solubility varies depending on the type of acid and on its concentration. Thus, in halo acids, the solubility increases markedly with acid concentration, a general order being HI > HBr > HCl. For nitric and phosphoric acids, solubility decreases up to about 8 mol dm acid, and then begins to increase. 

The biochemical reduction of a, -unsaturated -haloaliphatic acids by means of Clostridium kluyveri yielded halogen-free satmated acids. The same products were obtained from saturated -halo acids. However, the same microorganism converted ix, -unsaturated a-halo acids to saturated a-halo acids with R configuration. Yields of reduction of a-fluoro-, a-chloro- and a-bromocrotonic acid ranged from 30% to 100% [330]. 

---