Alcohols, primary with bromine

The bromination with alkali hypobromite in aqueous solution gives good results with (hetero)arylacetylenes, enynes (RCH=CHOCH) and diynes (RC=CC=CH) all acetylenes that are more acidic than those acetylenes in the aliphadc or cycloaliphatic series with an isolated triple bond. For the conjugated systems the hypobromite method is superior to the reaction of metallated acetylenes with bromine. Various acetylenic alcohols are also brominated smoothly, which can be explained in part by their better solubility in water. Since in the case of primary and secondary ethynyl alcohols, oxidation of the alcohol can occur, the use of an excess of hypobromite should be avoided. The best procedure is drop wise additon of a small shot measure of hypobromite ro a mixture of alcohol and water. If the bromoalkynes to be prepared are not too volatile, small amounts of THF or dioxane may be added to effect a better solubility of the alkyne in the aqueous phase. Addition of a co-solvent may also be desired when the starting compound is a solid (e.g. ethynylcyclohexanol). 

General Procedure for Selective Oxidation of Secondary Alcohols in Presence of Primary Alcohols by Treatment of Intermediate Tin Alkoxides with Bromine or Af-Bromosuccinimide... 

Better results are obtained on treatment of alcohols with bromine in dichloromethane solution in the presence of hexamethylphosphoric triamide (HMPA) and aqueous sodium bicarbonate. This reagent is highly selective for the oxidation of secondary alcohols in preference to primary alcohols [682]. 

Of the compounds we have dealt with so far, alcohols also dissolve in sulfuric acid. Alcohols can be distinguished from alkenes, however, by the fact that alcohols give a negative test with bromine in carbon tetrachloride and a negative Baeyer test—so long as we are not misled by impurities. Primary and secondary alcohols are oxidized by chromic anhydride, CrOa, in aqueous sulfuric acid within two seconds, the clear orange solution turns blue-green and becomes opaque. 

The reaction of trialkylboranes with bromine to give primary bromides is also induced with base, but in this case sodium methoxide in methanol is used as base in order to prevent an undesirable oxidative side reaction leading to alcohols.6 Two procedures have been employed. In one. bromine (33% excess) is added to the organoborane in THF followed by a solution of sodium methoxide in methanol, all at 0°. In the other, bromine and base (10% excess) are added simultaneously at 25°. The former procedure is preferable for monosubstituted olefins, the latter is preferable for hindered olefins. Apparently, in this case, all three alkyl groups are utilized since yields of primary bromides are 30-99%. 

Oxidation of sulfides. This oxide in combination with bromine has been used for selective oxidation of a secondary alcohol in the presence of a primary alcohol (7, 26 27). This mild procedure is also applicable to oxidation of sulfides (o sulfoxiilcs without further oxidation to sulfones (equation I). The method can also be used lo oxidi/c hydroxy sulfides to keto sulfoxides in one operation. The reageni also can be used lor oxidation of sidfenamides to sulfinamidcs without loi II union of sn I Iona in ides (eipial ion II). ... 

Oxidative Methods.—A convenient and inexpensive procedure for the oxidation of secondary alcohols to ketones, applicable to multi-mole preparations, uses aqueous sodium hypochlorite in acetic acid/ Selective oxidation of secondary alcohols is possible as primary alcohols are oxidized much more slowly. Alcohol oxidations with molecular bromine in combination with nickel(ll) benzoate in acetonitrile are remarkably free from competing reactions. However, 1,4-diols yield butyrolactones. ... 

Highly substituted alcohols are formed in the light-induced reaction of tri-alkylboranes with bromine in the presence of water. In common with the dark reaction, the initial process is one of a-bromination in the present case, migration from boron to carbon then occurs, both or only one of the alkyl groups migrating depending on whether the alkyl groups are primary or secondary, respectively (Scheme 128). 

When Acid Yellow 73 is dissolved in alcohol and treated, while warm, with bromine, four equivalents are absorbed to form Acid Red 87 (Eosine). This is used to a limited extent on wool its primary uses are for paper and inks. Other dyes related to Acid Red 87 are Acid Red 91 (dinitrodibromofluorescein). Acid Red 92 (Phloxine tetrabromotetra-chlorofluorescein), and Acid Red 51 (Erythro-sine tetraiodofluorescein). 

Bromine or chlorine dissolved in hexamethylphosphoric triamide [680-31-9] (HMPT) with a base, eg, NaH2PO, present, oxidizes primary and secondary alcohols to carbonyl compounds in high yield (38). 

Zinc chloride was used as a catalyst in the Friedel Crafts benzylation of benzenes in the presence of polar solvents, such as primary alcohols, ketones, and water.639 Friedel-Crafts catalysis has also been carried out using a supported zinc chloride reagent. Mesoporous silicas with zinc chloride incorporated have been synthesized with a high level of available catalyst. Variation in reaction conditions and relation of catalytic activity to pore size and volume were studied.640 Other supported catalytic systems include a zinc bromide catalyst that is fast, efficient, selective, and reusable in the /wa-bromination of aromatic substrates.641... 

Porco s route to (—)-kinamycin C (3) began with 2,5-dihydroxybenzaldehyde (38), which was elaborated to the enone 35 by the sequence shown in Scheme 3.6. Regioselective bromination [25] followed by methylation and reduction of the aldehyde function afforded the primary alcohol 39. The alcohol 39 was dearomatized by treatment with bis(acetoxy)iodobenzene, to afford the quinone monoketal 41. Transketalization with 1,3-propanediol followed by silylation of the primary alcohol generated the silyl ether 42 in 72 % yield over three steps. 

N-bromoacetamide org chem CHsCONHBr Needlelike crystals with a melting point of I02-I05°C soluble in warm water and cold ether used as a brominating agent and in the oxidation of primary and secondary alcohols. en bro mo-3 sed-3,mTd ... 

Oxidation and Reduction.—A number of selective oxidation procedures have been reported. Trichloroacetaldehyde on dehydrated chromatographic alumina converts the diol (15) into the 3/3-hydroxy-17-ketone (68%)." Primary alcohols are reported to be less readily oxidized than secondary alcohols by this reagent. Similarly, bromine or chlorine with HMPA oxidizes secondary alcohols more readily than primary alcohols. Thus the diol (16) was converted into the ketol (17)... 

Very recently, Hu et al. claimed to have discovered a convenient procedure for the aerobic oxidation of primary and secondary alcohols utilizing a TEMPO based catalyst system free of any transition metal co-catalyst (21). These authors employed a mixture of TEMPO (1 mol%), sodium nitrite (4-8 mol%) and bromine (4 mol%) as an active catalyst system. The oxidation took place at temperatures between 80-100 °C and at air pressure of 4 bars. However, this process was only successful with activated alcohols. With benzyl alcohol, quantitative conversion to benzaldehyde was achieved after a 1-2 hour reaction. With non-activated aliphatic alcohols (such as 1-octanol) or cyclic alcohols (cyclohexanol), the air pressure needed to be raised to 9 bar and a 4-5 hour of reaction was necessary to reach complete conversion. Unfortunately, this new oxidation procedure also depends on the use of dichloromethane as a solvent. In addition, the elemental bromine used as a cocatalyst is rather difficult to handle on a technical scale because of its high vapor pressure, toxicity and severe corrosion problems. Other disadvantages of this system are the rather low substrate concentration in the solvent and the observed formation of bromination by-products. 

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