Chlorohydrins, from alkenes

Formation of chlorohydrins from alkenes Chlorination with solvent participation and cyclization Formation of chlorohydrins in acidic aqueous solution. 

ELECTROPHILIC ADDITIONS TO CARBON-CARBON MULTIPLE BONDS A. Chlorinating agents Sodium hypochlorite solution 7V-Chloro succi n i m i de Antimony pentachloride Formation of chlorohydrins from alkenes Chlorination with solvent participation and cyclization Controlled chlorination of acetylenes... 

Miscellaneous Reactions. DTBP has been used as a hydrosi-lylation catalyst, even though catalysis by transition metal complexes have largely replaced the radical methods. DTBP has also been used as an oxidant for silanes. Other applications of DTBP include its use as an initiator for radical mediated deoxygenation of alcohols via the corresponding chloroformate or acetate ester (eq 20). It has also been used as an initiator for the reduction of lactones and esters to ethers using trichlorosilane. In a rare example of a nonradical reaction, DTBP has been used in conjunction with titanium(IV) chloride for the formation of chlorohydrin from alkenes (eq 21). ... 

Halohydrins are /J-halogenated alcohols. They can be obtained in H20-containing solvents from alkenes and reagents, which transfer Hal ions. N-Broniosuccinnuide (transfers Br Figures 3.43 and 3.44 as well as 3.47), chloramine-T (transfers Cl Figure 3.46), and elemental iodine (transfers I Figure 3.47) have this ability. Bromonium and chloronium ions react with H20 via an SN2 mechanism. This furnishes the protonated bromo- or chlorohydrins, which are subsequently deprotonated. 

For addition of HOC1 the olefins are stirred with 0.125-0.5 m-HOCl at 10°. The yields of chlorohydrin from 1-alkenes of higher molecular weight are considerably increased by addition of pyridine and sulfuric acid (initial pH 6-6.5)278. Chlorohydrins of higher molecular weight are also, accessible by reaction of alkyl hypochlorites with the olefin in an aqueous medium tert-butyl hypochlorite (a yellow oil, b.p. 77-78°/760 mm) is suitable for this purpose it is obtained by passage of chlorine into tert-butyl alcohol in aqueous sodium hydroxide at 0-20°. 

One method for the preparation of epoxides from alkenes involves (1) treating the alkene with chlorine or bromine in water to form a chlorohydrin (or bromohydrin) followed by (2) treating the halohydrin with a base to bring about intramolecular displacement of Cl . These steps convert propene first to l-chloro-2-propanol and then to methyloxirane (propylene oxide). 

Chlorohydrin B, prepared from alkene A by addition of Cl and OH, is converted to epoxide C with base. C is converted to estrone in one step. 

OL-Alkenylcarbinols Reduction of alkynyl chlorohydrins, readily available from reaction of a-chloro ketones with lithium acetylides, with lithium aluminum hydride and sodium methoxidc results in partial reduction of the triple bond as well as a facile rearrangement to provide a-alkenylcarbinols. One useful feature is that only (E)-disubstitutcd alkenes are formed. The addition and reductive rearrangement can be conducted in a single operation. 

The essence of the Wacker process is the invention of the reoxidation process for Pd° by using CuCh as a cocatalyst. Cu" salts are good reoxidants, but chlorination of carbonyl compounds takes place with CuCh. For example, chloroacetaldehyde is a by-product of the Wacker process. Chlorohydrin is another by-product from the reaction of ethylene with PdCh and CuCb. - Thus, a number of other reoxidants were introduced. When CuCl, pretreated with oxygen, is used, no chlorination of ketones takes place and the rate of the reaction is higher. - Also Cu(N03)2 and Cu(OAc)2 have been used. Oxidation of cy-clopentene with PdCl2/Fe(C104)3 combined with electrochemical oxidation was carried out. Benzoqui-none was used at first by Moiseev et al and later by many other researchers as a good reoxidant, but a stoichiometric amount is necessary. The oxidation of alkenes can be carried out smoothly with catalytic... 

Ethylene chlorohydrin (38) is formed in the Wacker process as a byproduct. Chlorohydrins are obtained as main products when PdCl3 (pyridine) is used [29]. The optically active chlorohydrin 40 with high ee was obtained without forming the regioisomer 41 from allyl phenyl ether (39) and other substituted alkenes when the bimetallic Pd complex 42 coordinated by water soluble chiral BINAP-based ligand 43 (II-9) was used [30]. 

Epoxides are important feedstock chemicals. Currently the Cs-Cg epoxides are prepared from the corresponding alkenes by the ARCO chlorohydrin process, which produces chlorinated organics and stoichiometric sodium chloride as... 

Oxirans.—A simple four-stage preparation of (5)-propylene oxide from ethyl L-( —)-maleate has been described (Scheme 2). This work is of importance for the synthesis of nonactin carboxylic acid. Another synthesis of optically-active propylene oxide involves the cyclization of OL-propylene chlorohydrin with a variety of bases in the presence of a cobalt complex the highest optical purity was 27%. Wynberg and co-workers have shown that the base-catalysed epoxidation of electron-poor alkenes is subject to catalytic asymmetric induction hydrogen peroxide and t-butyl hydroperoxide were used as oxidants in the presence of quaternary... 

The creation of a bromonium ion in alkene brominations suggests that, in the presence of other nucleophiles, competition might be observed in the trapping of the intermediate. For example, bromination of cyclopentene in water as solvent gives the vicinal bromoalcohol (common name, bromohydrin). In this case, the bromonium ion is attacked by water, which is present in large excess. The net transformation is the anti addition of Br and OH to the double bond. The other product formed is HBr. The corresponding chloroalcohols (chlorohydrins) can be made from chlorine in water through a chloronium ion intermediate. 

Shibasaki et al. developed a method for the direct synthesis of chlorohydrins or 2-acetoxy alcohols from disubstituted olefins [41). Various kinds of chlorohydrins are prepared from the corresponding alkenes with bis(trimethylsilyl)peroxide (BTSP) and chlorotrimethylsilane (TMSCl) in the presence of the catalyst (SnCU or (SnO) ). It is worth noting that 2-acetoxy alcohols could be obtained under similar reaction conditions using trimethylsilyl acetate (TMSOAc) instead of TMSCl with the promotion of Zr(0 Pr)4 in place of SnCU (Scheme 10.20). 

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