Formation of chlorohydrins

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... 

A stereochemical study reported by Henry illustrated that the formation of aldehyde and formation of chlorohydrin occur with different stereochemistry, and this result implies that one process occurs by syn addition and one by anti addition of water and palladium across the olefin. This study is summarized in Scheme 16.24. Oxidation of the non-race-mic, chiral allyl alcohol in the absence of added chloride forms the (R)-(E)-alcohol, whereas reaction of the allyl alcohol in the presence of added chloride forms the product with stereochemistry resulting from the opposite mode of attack. Because it is known that the allylic alcohol binds to palladium with hydrogen bonding between the hydroxyl group and the bound chloride, Henry concluded that the reaction conducted in the presence of high concentrations of added diloride occurs by external attack of the oxygen nucleophile, while the reaction with low concentrations of added chloride occurs by insertion of the olefin into a Pd-0 bond. ... 

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). ... 

Chlorohydrination. The mechanism for the formation of propylene chlorohydrin is generally beheved to be through the chloronium ion intermediate (109,112). 

The l-chloro-2-propanol isomer represents about 85% of the chlorohydrin produced. In order to minimise the formation of dichlotide coproduct and ether, the reactant compositions are chosen such that the effluent Hquid contains 4—5 wt % propylene chlorohydrin. Under these conditions, the yield of chlorohydrin, dichloride, and ether from the reactants is reported to be 87—90, 6—9, and 2%, respectively (109,110,112). 

Benzyl chloride readily forms a Grignard compound by reaction with magnesium in ether with the concomitant formation of substantial coupling product, 1,2-diphenylethane [103-29-7]. Benzyl chloride is oxidized first to benzaldehyde [100-52-7] and then to benzoic acid. Nitric acid oxidizes directly to benzoic acid [65-85-0]. Reaction with ethylene oxide produces the benzyl chlorohydrin ether, CgH CH20CH2CH2Cl (18). Benzylphosphonic acid [10542-07-1] is formed from the reaction of benzyl chloride and triethyl phosphite followed by hydrolysis (19). 

Epoxide formation from chlorohydrins is marked by an increase in rate with alkyl substitution (28) as shown in Figure 1. This phenomenon has been explained on the basis that steric crowding ia the chlorohydrin is somewhat reheved as the epoxide is formed, so that the greatest rehef of strain results from ring closure of the most crowded chlorohydrin (28). 

Formation of Cyclic Carbonates. In the absence of water, chlorohydrins such as 2-chloroethanol and l-chloro-2-propanol react with an alkah carbonate or bicarbonate to produce cycHc carbonates such as ethylene carbonate [96-49-1] and propylene carbonate [108-32-7] ia yields of up to 80%... 

Since the formation of the chlorohydrin is accompanied by the production of an equimolar quantity of hydrogen chloride [7647-01 -OJ, the reaction solution is strongly acidic and corrosive. The first chlorohydrin reaction towers were built of stoneware or of mild steel and lined with mbber and ceramic tiles. More recently corrosion-resistant reinforced plastics have been used with good results, but operating pressures must be maintained at or near atmospheric. 

Ghlorohydrination with Nonaqueous Hypochlorous Acid. Because the presence of chloride ions has been shown to promote the formation of the dichloro by-product, it is desirable to perform the chlorohydrination in the absence of chloride ion. For this reason, methods have been reported to produce hypochlorous acid solutions free of chloride ions. A patented method (48) involves the extraction of hypochlorous acid with solvents such as methyl ethyl ketone [78-93-3J, acetonitrile, and ethyl acetate [141-78-6J. In one example hypochlorous acid was extracted from an aqueous brine with methyl ethyl ketone in a 98.9% yield based on the chlorine used. However, when propylene reacted with a 1 Af solution of hypochlorous acid in either methyl ethyl ketone or ethyl acetate, chlorohydrin yields of only 60—70% were obtained (10). 

Like the formation of a-cyanohydrins, this reaction is catalyzed by bases or cyanide ion, but unlike the a-cyanohydrin case this reaction is not reversible, and under certain conditions it can proceed with violence. Ethylene cyanohydrin can also be prepared by the reaction of ethylene chlorohydrin and alkaH cyanides (39). 

The disadvantage of the chlorohydrin process is the use of toxic, corrosive, and expensive chlorine the major drawback of the peroxide process is the formation of co-oxidates in larger amounts than the desired PO. The direct epoxidation of propylene using 02 (i.e., partial oxidation of propylene) from air has been recognized as a promising route. 

Commercial ethylene chlorohydrin is dried over anhydrous sodium sulfate and distilled before use b.p. 126-127°(743 mm.). Excess is used to avoid the formation of dibenzhydryl ether as a by-product. 

For 1,2-disubstituted epoxides, the regiochemical outcome of nucleophilic attack becomes less predictable. However, in the case of epoxy ethers chelation control can be used to deliver the nucleophile preferentially to the epoxide carbon away from the ether moiety. Thus, treatment of epoxy ether 61 with an imido(halo)metal complex, such as [Cr(N-t-Bu)Cl3(dme)], leads to the clean and high-yielding production of the chlorohydrin 64. The regioselectivity is rationalized in terms of initial formation of a chelated species (62), followed by attack at C-3 to form the more stable 5-membered metallacyclic alkoxide 63 <00SL677>. 

The 2-chloroethyl group, which is often an effective toxo-phore, was then attached to phosphorus through oxygen. No reaction appeared to take place between ethylene chlorohydrin and diethyl phosphorochloridate in the absence of a tertiary base. In the presence of pyridine, however, which removed the hydrogen chloride formed, a smooth reaction took place at 0° with the formation of diethyl 2-chloroethyl phosphate,... 

The stepwise formation of epoxides through the reaction of alkenes with sodium hypochlorite with, or without, the isolation of the intermediate chlorohydrin has been subjected to catalysis with (V-benzylquininium chloride under liquiddiquid two-... 

The original preparation of y-crotonolactone by Lespieau involved a five-step sequence from epichlorohydrin and sodium cyanide. A recent detailed study of this procedure reported an overall yield of 25% for the lactone. Glattfeld used a shorter route from glycerol chlorohydrin and sodium cyanide hydrolysis and distillation of the intermediate dihydroxy acid yielded y-cro-tonolactone in 23% yield and -hydroxy-y-butyrolactone in 28% yield. The formation of y-crotonolactone in 15% yield has also been reported from pyrolysis of 2,5-diacetoxy-2,5-dihydrofuran at 480-500 . ... 

One ocher reaction noc shown is the formation of propylene dichloride. The demand for this compound is generally insufficient to absorb all the coproduction, so it also ends up on the list of things to be disposed of coming from the PO-chlorohydrin process, But despite this and all the ocher problems already mentioned about the chlorohydrin route, the process remains economically healthy—breathing heavily, but healthy. Indeed, 40 to 50% of the PO produced in the United States comes from this route. 

Two of the reactions calce place in the same reactor in this plant. The formation of the hypochlorous acid (HOCl) from chlorine and water, and the reaction with propylene all occur simultaneously on the left in Figure 11—2. Propylene reacts readily with chlorine to form that unwanted by-product, propylene dichloride. To limit that, the HOCl and HCl are kept very dilute. But as a consequence, the concentration of the propylene leaving the reactor is very low—only 3—5% Ac any higher concentration, a separate phase or second layer in the reactor would form. It would preferentially suck up (dissolve) the propylene and chlorine coming in, leading to runaway dichloride yields. The low concentration levels of the propylene chlorohydrin and the need to recycle so many pounds of material is the reason the process is so energy intensive. It just takes a lot of electricity to pump all that stuff around. 

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