Halogeno-alcohols

Lower aliphatic primary alcohols including octanol, halogeno alcohols, and benzylic alcohols yield only alkyl fluorides [81, 82 The reaction of higher primary alcohols gives a mixture of fluorides and alkyl 2,3,3,3-tetrafluoropropionates [S3] and 2-nitro alcohols, alcohols branched at C-2 [82, 84 and unsaturated alcohols [55] give 2,3,3,3-tetrafluoropropionates exclusively... 

Halides (confined at present to silver halides) can be deposited by hydrolyzing a water-soluble halogeno-alcohol (halohydrin) to slowly form halide ions in the presence of Ag ions ... 

Precursor y-halogeno alcohols are frequently prepared by the classic sequence of addition of hydrogen halide to a,/3-unsaturated aldehydes, ketones, acids or esters, followed by Grignard reaction or hydride reduction. Recently a novel and general synthesis of 3-methoxyoxetanes from 3-phenylseleno-2-propenal was reported. This method comprises a sequence of Grignard addition to the aldehyde function, treatment with two equivalents of MCPBA, and then reaction with methanolic sodium hydroxide (equation 78) (80JOC4063). 

A very promising synthesis of /3-lactones has been recently reported, involving the palladium-catalyzed carbonylation reaction of halogeno alcohols. For example, 3-phenyl-2-oxetanone was obtained in 63% yield from 2-phenyl-2-bromoethanol in DMF solution at room temperature under 1 atmosphere pressure of carbon monoxide (equation 115). A proposed mechanism, in which palladium metal inserts into the carbon-halogen bond, followed by insertion of a molecule of carbon monoxide into the carbon-palladium bond and then ring closure, fits kinetics data (80JA4193). 

Mizuno K, Mabuchi K, Miyagawa T, Matsuda Y, Kita S, Kaida M, Shindo Y. 1997. IR study of hydrogen bonds in halogeno-alcohol-water mixtures. J Phys Chem A 101 1366-1369. 

The intermediates 196 have been reacted with cu-halogeno-alcohols (197) to give N-carboxylsulphamates (198) (equation 47)230. Cyclization of 198 can occur very easily in the presence of triethylamine to give a new family of 2-oxazolidones (199) (equations 48 and 49). 

Reaction of the halogeno-alcohols (573) and (574) with potassium t-butoxide in DMSO gave the dioxan derivative (575) as the major product, plus small amounts of the bond-shift isomer of (575) and the ethylene acetal of bicyclo[3,2,l]oct-3-en-2-one. The elimination of hydrogen halide from (573) or (574), therefore, generates predominantly the bicycloalkyne and only small amounts of the bicycloallene the products are derived from the intramolecular nucleophilic addition of the side-chain alkoxide to the tt-centres in these reactive intermediates. 

If X is more strongly nucleophihc (e.g., X = halogenide), its attack competes with H2O (e.g., in aqueous hydrohalogenic acid) giving rise to formation of 2-halogeno alcohols (halohydrins) as products. 

Almost insoluble in cold water. Higher alcohols (including benzyl alcohol), higher phenols (e.g., naphthols), metaformaldehyde, paraldehyde, aromatic aldehydes, higher ketones (including acetophenone), aromatic acids, most esters, ethers, oxamide and domatic amides, sulphonamides, aromatic imides, aromatic nitriles, aromatic acid anhydrides, aromatic acid chlorides, sulphonyl chlorides, starch, aromatic amines, anilides, tyrosine, cystine, nitrocompounds, uric acid, halogeno-hydrocarbons, hydrocarbons. 

A few studies on solvolyses by alcohols and by water are available. The hydrolyses studied include displacement of alkylamino groups from acridine antimalarials and of halogen from other systems. In all cases, these reactions appeared to be first-order in the heterocyclic substrate. By a detailed examination of the acid hydrolysis of 2-halogeno-5-nitropyridine, Reinheimer et al. have shown that the reaction rate varies as the fourth power of the activity of water, providing direct evidence that the only reactive nucleophile is neutral water, as expected. 

Okamoto et al. found that A-oxidation activates 4-halogeno-quinolines in the reaction with piperidine in aqueous alcohol by kinetic factors of 9 to 25, at 100°. This rate-enhancing effect is accompanied by a fairly large decrease in the enthalpy of activation (up to 10 kcal/mole in the chloro compounds), the effect of which is partly offset by a decrease in the entropy of activation. 

Halogeno-4-nitropyridine-X -oxide Et2NH in alcohol, reflux temp. 1 -2 -0.3 125... 

The catalytic effect of protons has been noted on many occasions (cf. Section II,D,2,c) and autocatalysis frequently occurs when the nucleophile is not a strong base. Acid catalysis of reactions with water, alcohols, mercaptans, amines, or halide ions has been observed for halogeno derivatives of pyridine, pyrimidine (92), s-triazine (93), quinoline, and phthalazine as well as for many other ring systems and leaving groups. An interesting displacement is that of a 4-oxo group in the reaction of quinolines with thiophenols, which is made possible by the acid catalysis. 

The enhanced reactivity of 5-halogeno-l,2,4-thiadiazoles over 3-halogeno-l,2,4-thiadiazoles has been mentioned before (see Section 5.08.7.1). Nucleophilic substitution at this center is a common route to other 1,2,4-thiadiazoles, including 5-hydroxy, alkoxy, mercapto, alkylthio, amino, sulfonamido, hydrazino, hydroxylamino, and azido derivatives. Halogens in the 3-position of 1,2,4-thiadiazoles are inert toward most nucleophilic reagents, but displacement of the 3-halogen atom can be achieved by reaction with sodium alkoxide in the appropriate alcohol <1996CHEC-II(4)307>. 

When electronegative substituents are present, oxadiazoles undergo nucleophilic reactions on the carbon atoms, both in position 3 or 5- The substitution of halogen, alkoxy and trichloromethyl derivatives has. been studied. 5-Halogeno-oxadiazoles react with ahphatic and aromatic primary and secondary amines, to give the corresponding amino-derivatives. With sodium hydroxide and -alcoholate, hydroxy and alkoxy oxadiazoles are obtained 25 a, 55 b). 

In alkaline media, 3-halogeno compounds appear to be less stable 3-chloro-5-phenyl-l,2,4-thiadiazole is decomposed completely by 1 Jf-alcoholic potassium hydroxide and by hydrazine.178 Nucleophilic substitution of the 3-halogen atom by alkoxy groups can be achieved, however, by means of sodium alkoxide in the appropriate alcohol 3-methoxy-, 3-benzyloxy-, and 3-(2 -hydroxyethoxy)-5-phenyl-l,2,4-thiadiazole are obtainable by this route in good yield.178... 

Borazines, particularly polymeric compounds, have been extensively investigated as preceramic materials from which coatings and fibers of boron nitride can be produced upon thermolysis. B-aryl and halogeno-amino borazines are reported to have use as fire retardants in cotton and nylon textiles. Other reported uses for borazines are as epoxy resin catalysts, polymerization inhibitors of unsaturated alcohols and esters, and catalysts for polymerization of alkenes (95). 

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