Ethylene oxide General scheme

Functionalization of these reactive anionic chain ends can be achieved by a variety of methods all based on the general concepts of carbanion chemistry. For example, reaction with C02 or succinnic anhydride leads to the carboxy terminated derivatives [10], while hydroxy-terminated polymers can be easily obtained by reaction with ethylene oxide (Scheme 3) [11]. In select functionalization reactions, such as alkylation with p-vinyl benzyl chloride, the nucleophilicity of the carbanionic species may be necessary and this can be achieved by reaction of the chain end with 1,1-diphenylethene followed by functionalization [12,13]. 

Melphalan and the racemic analog have been prepared by two general routes (Scheme I). In Approach (A) the amino acid function is protected, and the nitrogen mustard moiety is prepared by conventional methods from aromatic nitro-derivatives. Thus, the ethyl ester of N-phthaloyl-phenylalanine was nitrated and reduced catalytically to amine I. Compound I was reacted with ethylene oxide to form the corresponding bis(2-hydroxyethyl)amino derivative II, which was then treated with phosphorus oxychloride or thionyl chloride. The blocking groups were removed by acidic hydrolysis. Melphalan was precipitated by addition of sodium acetate and was recrystallized from methanol. No racemization was detected [10,28—30]. The hydrochloride was obtained in pure form from the final hydrolysis mixture by partial neutralization to pH 0.5 [31]. Variants of this approach, used for the preparation of the racemic compound, followed the same route via the a-acylamino-a-p-aminobenzyl malonic ester III [10,28—30,32,33] or the hydantoin IV [12]. 

Pd(II) can be expressed by the following general schemes. As a whole, two hydrogens are abstracted from two substrates A-H and B-H, generating Pd(0) and the product A-B. This reaction is stoichiometric with Pd(II), but the reaction becomes catalytic when Pd(0) is oxidized in situ to Pd(II) with appropriate oxidants (OX), and the whole reaction can be summarized by a third equation. For example, formation of vinyl acetate from ethylene and oxidative coupling of benzene can be understood formally as dehydrogenation reactions. These oxidative reactions using Pd(ll) are considered in Chapter 2. 

The reactions of f-butyl peroxylate anion with ethyl 2-methylene-3-acetoxy-butanoate and with ethyl 2-bromomethylbut-2-enoate have been studied by Mailard and co-workers, respectively (Scheme 3.134). " They found that both reactions resulted in the y-attack products 311 in low yields. However, the allyl f-butyl peroxides 312 were obtained in 45% yield when the reaction was carried out in the presence of poly(ethylene oxide) 400. Subsequently, 312 was converted into the corresponding glycidic ester 313 by heating in benzene. Recently, Chen et al. developed the first peroxo-asymmetric allylic alkylation of bulky hydroperoxyalkanes with MBH carbonates with catalysis by commercially available modified cinchona alkaloids. Peroxides 314 were generally... 

Other interesting articles and reviews include polyvinyl alcohol composites, generally [62], with proteins [63-65], starch [66], chitosan [67], simple sugars [68], and a Baeyer Villiger oxidation [95] (Scheme 3) of a an ethylene-vinyl alcohol copolymer to produce a biodegradable polyhydroxypolyester. 

Scheme 4. General scheme for ethylene glycol oxidation on Pt-based catalysts in acidic media. 

Apparent anomalies in reactivity have appeared to exist for a number of reactions. It is not generally known that under conventional EQ conditions, an electrophile can promote aromatic metalation during the quench step. It was stated in an early report [130] that the reaction of phenothiazine 31 with 2 equivalents of n-BuLi proceeds with formation of dilithio intermediate 33 via monoUthio amide 32 (Scheme 26.8). The fact that the regioselectivity of the reaction is dependent on the electrophile used was not properly analyzed by the authors whereas trapping experiments with RCOX=DME, PhCONMe, MeCO Li, PhCO Li, and CO give C(7j-acylation products 34, the reaction of RX = MeCOCl, Mel, and ethylene oxide provides lVjf70)-substitution products 35. 

Poly(ethylene oxide)s of low molecular weight, i.e., below about 3000, are generally prepared by passing ethylene oxide into ethylene glycol at 120—150°C and about 3 atmospheres pressure, using an alkaline initiator such as sodium hydroxide. Anionic polymerization proceeds according to the following scheme Initiation... 

Scheme 7.8 is a general reaction scheme for the copolymerization of ethylene oxide and propylene oxide with multifunctional alcohols as initiators. 

This class of surfactant has been extensively investigated because it has the potential to combine the advantages of both the anionic and nonionic surfactant types. In general the ethoxylation of the fatty alcohol is not carried sufficiently far to produce a truly water-soluble nonionic surfactant usually five or fewer molecules of ethylene oxide are added and the unsulfated material is still of limited solubihty in water. The water-insoluble nonionic material, however, can then be sulfated with chlorosulfonic acid or SO3 and neutralized, usually with sodium hydroxide, to yield the desired product. Other counterions may be employed by slight modifications of the reaction or by the use of alternative reaction schemes. 

In Europe, where an abundant supply of anthracene has usually been available, the preferred method for the manufacture of anthraquinone has been, and stiU is, the catalytic oxidation of anthracene. The main problem has been that of obtaining anthracene, C H q, practically free of such contaminants as carbazole and phenanthrene. Many processes have been developed for the purification of anthracene. Generally these foUow the scheme of taking the cmde anthracene oil, redistilling, and recrystaUizing it from a variety of solvents, such as pyridine (22). The purest anthracene may be obtained by azeotropic distillation with ethylene glycol (23). 

The relative rate constants (fe ) do not account for the fact that approach of the nitrile oxide to the 7i-bond can occur from both olefinic diastereofaces with two regioisomeric modes of reaction (Scheme 6.14). In the case of achiral 1-alkenes, only one regioisomer is formed. With chiral dipolarophiles, preference for one of the two is usually found (diastereodifferentiation). The relative diastereofacial reactivity (fejH) is used to evaluate this effect (121). With ethylene, there are four possibilities of attack (two for each face corresponding to the different regio-isomers), and the of each is set as 0.25. In diastereodifferentiating cycloadditions, such as those with a-chiral alkenes, the major isomer generally results... 

In general, the ethylene to ethane selectivity is governed by the relative rates of the processes shown in Scheme 3.1. Here, combination of methyl radicals (step 2) is a homogeneous process, but all other steps can be both homogeneous and heterogeneous.294 It was also found that further oxidation of the C2 products (steps 4 and 6) becomes important only with increasing C2 concentration in the system.327... 

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