Secondary alcohols bromine

A white solid, m.p. 178 C. Primarily of interest as a brominaling agent which will replace activated hydrogen atoms in benzylic or allylic positions, and also those on a carbon atom a to a carbonyl group. Activating influences can produce nuclear substitution in a benzene ring and certain heterocyclic compounds also used in the oxidation of secondary alcohols to ketones. 

And in the recipe above, Vogel want s to get rid of a secondary alcohol just like the one on MD-P2Pol and replace it with a bromine. Wait a minuter you may say, That isn t a double bond like... 

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). 

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 ... 

A combination of bromide ions and methyl octyl sulphide is able to oxidise secondary alcohols at the potential necessary to fonn bromine. Conversion of the alcohol to the ketone follows the Scheme 8.2 and uses an undivided cell with benzo-nitrile as the solvent containing 2,6-lutidine as base and tetraethylamnionium bromide. The reaction occurs using a platinum anode at 1.1 V vs-, see [28], Thio-anisole alone, in absence of bromide, will function as a catalyst for the oxidation of secondary alcohols but in these cases a more positive anode potential of 1.5 V vs. see is needed to oxidise the thioether [29]. 

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. 

The transformation is also possible with hexamethyldisilane and pyridinium bromide perbromide as the source of bromine. This reaction, however, is slower in the case of primary and secondary alcohols. Benzylic, allylic, and tertiary alcohols react rapidly. Hence selective reactions are possible. In the case of secondary alcohols, the conversion occurs with 88% inversion. 

Other reagents, providing a source of electrophilic halogen, able to selectively oxidize secondary alcohols include molecular chlorine,13 molecular bromine,13c 3-iodopyridine dichloride,13a trichloroisocyanuric acid (TCIA),14 the complex HOF MeCN15 and tetraethylammonium trichloride.16... 

The selective oxidation of the secondary alcohol is performed by dropping a bromine solution on a mixture of (Bu3Sn)20 and the diol in CH2CI2. Although, no complete formation of bis-tin alkoxide is secured and the generated HBr—that may cause the hydrolysis of tin alkoxides—is not quenched, a useful yield of hydroxyketone is obtained. 

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

Promotion of an SN2 displacement mechanism, and hence greater regioselectivity, may be effected by the addition of liquid bromine to a warm suspension of purified red phosphorus in the appropriate alcohol. The reaction is of general application with primary alcohols (isobutyl alcohol to hexadecan-l-ol) the yields are over 90 per cent of the theoretical, but with secondary alcohols the yields are in the range 50-80 per cent (Expt 5.55). This method is to be preferred to the direct use (rather than the in situ generation) of phosphorus tribromide which is the more hazardous reagent. The outline mechanism may be represented thus ... 

Thus, 3-methylthiophene is brominated with NBS to give 2-bromo-3-methyl-thiophene (cf Figure 16) which is then metallated with n-butyllithium. The lithiated thiophene is activated with TMEDA and then coupled with 3,7,11-trimethyldodecanal. The coupled product contains a secondary alcohol which is... 

Cinnamyl alcohols such as 95 were converted to the corresponding oxetane 96 by reaction with bis-(collidine)bromine(l) hexafluorophosphate (Equation 32) via a 4- r/o-/r7g-electrophilic cyclization <1999JOC81, 2001TL2477>. High yields of oxetanes (up to 88%) were only achieved with tertiary alcohols, with secondary alcohols giving mainly degradation products. 

Bromine dehydrogenates alcohols to carbonyl compounds [682, 726, 729, 734] (secondary alcohols in preference to primary alcohols [682]) and hydrazo compounds to azo compounds [733] and oxidizes sulfides to sulf-... 

Similar selectivity is found with chlorine (or bromine) in the presence of hexamethylphosphoric triamide (HMPA). The addition of solutions of chlorine in chloroform to stirred solutions of the alcohols in a mixture of HMPA, dichloromethane, and an aqueous solution of sodiunfdihydrogen phosphate at 0-5 °C results in very good yields of ketones. Competitive experiments with equimolar mixtures of primary and secondary alcohols show a 95-97% predominance of ketones over aldehydes [682]. 

Like chlorine, bromine is used to convert secondary alcohols into ketones. A convenient way is to apply the addition product of 2 mol of bromine with l,4-diazabicyclo[2,2,2]octane (Dabco), a nonhygroscopicyellow solid, prepared by mixing carbon tetrachloride solutions of bromine and Dabco. The compound decomposes at 155-160 °C [726]. Oxidation with this addition product is carried out in acetonitrile solution at 50 °C and results in 50 and 71% yields of cyclopentanone and cyclohexanone, respectively, but very low yields of 2-pentanone [726]. 

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]. 

The platinum-catalyzed oxidation with oxygen can also be applied for selective oxidation of secondary alcohols if no primary alcohol is present [73]. Like the tin-bromine method, axial secondary hydroxy groups will undergo preferential oxidation over equatorial hydroxy groups. However, as described above large amounts of platinum metal are required for these oxidations. Some improvement in catalyst activity has been achieved by promotion of platinum with bismuth or lead [76]. This also causes a change in selectivity and makes it possible in... 

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. 

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