Etherification kinetics

Chemical Properties. Neopentyl glycol can undergo typical glycol reactions such as esterification (qv), etherification, condensation, and oxidation. When basic kinetic studies of the esterification rate were carried out for neopentyl glycol, the absolute esterification rate of neopentyl glycol with / -butyric acid was approximately 20 times that of ethylene glycol with / -butyric acid (7). 

The kinetic resolution by etherification has also been conducted through the cyclization of epoxy aliphatic alcohols.274 In these reactions catalyzed by monomeric complex 51, the ring closure of acyclic substrates occurred with exclusive / -selectivity (Equation (74)), whereas m -openings were observed in the desymmetrization of... 

The highly hydrophilic alcohols, pentaerythritol and 2-ethyl-2-hydroxymethyl-propan-l,3-diol, can be converted into their corresponding ethers in good yields under phase-transfer catalytic conditions [12]. Etherification of pentaerythritol tends to yield the trialkoxy derivative and kinetics of the reaction have been shown to be controlled by the solubility of the ammonium salt of the tris-ether in the organic phase and the equilibrium between the tris-ether and its sodium salt [13]. Total etherification of the tetra-ol is attained in good yield when reactive haloalkanes are used, and tetra-rt-octylammonium, in preference to tetra-n-butylammonium, bromide [12, 13]. 

The explanation for the fact that the obtained PSU contains only vinylbenzyl chain ends, even when the etherification is performed in methylene chloride as reaction solvent, is provided by the kinetic particularities outlined below ... 

Catalysts lacking phosphorus ligands have also been used as catalysts for allylic substitutions. [lr(COD)Cl]2 itself, which contains a 7i-accepting diolefin ligand, catalyzes the alkylation of allylic acetates, but the formation of branched products was only favored when the substitution reaction was performed with branched allylic esters. Takemoto and coworkers later reported the etherification of branched allylic acetates and carbonates with oximes catalyzed by [lr(COD)Cl]2 without added ligand [47]. Finally, as discussed in Sect. 6, Carreira reported kinetic resolutions of branched allylic carbonates from reactions of phenol catalyzed by the combination of [lr(COE)2Cl]2 and a chiral diene ligand [48]. 

Because of the high stability of the ether function, etherification of unprotected sucrose leads to a kinetic distribution of products directly reflecting the relative reactivity of the hydroxyl groups. This reaction is therefore the best probe for reactivity studies at least for discussing the relative rates of the first substitution. The following substitutions are more difficult to compare, since supplemental factors (electronic and steric) arising from the first substitution interfere with the natural reactivity order of unprotected sucrose. 

Table 8.2. Kinetic parameters for the reaction rate expressions of esterification/etherification of hexanoic acid and 1-octanol (as determined by Ref. [29] Kwater from Ref. [30]).

Thus the reaction of sodium eugenoxide with various alkyl iodides in dry alcohol solution was shown to be in accord with second-order kinetics.1 The reaction of sodium ethoxide with optically active 2-bromo or 2-chlorooctane proceeded with complete inversion,2 and etherification of ethanol containing O18 with diethyl sulfate and alkali indicated that the ethyl group came from the sulfuric ester and that the alkoxide fragment was derived from the alcohol.8... 

The relative rates of olefin production and etherification have been shown to vary with reaction conditions (99-101), including temperature and contact time, and with the geometry of the catalyst pore system (99). Bryant (99) has demonstrated kinetic effects in ethanol and n-butanol dehydration that greatly favor olefin formation using a series... 

The water cooled tubular reactor (WCTR) represents the optimal solution for the etherification because it is the best compromise between kinetics and thermodynamics [7]. The Snamprogetti (now Saipem) WCTR (Figure 11.5) is a bundle-type heat exchanger with the catalyst in the tube side and the tempered cooling water flowing co-current or counter-current in the shell side. The catalyst is self-supporting in the bottom shell of the reactor, in the tubes and above the upper tube sheet. 

Analysis of the uptake/unit time results has indicated that several reactions take place simultaneously, and that such additives as the alkali chlorides or urea increase the rate of reaction. Another kinetic study concluded that, in the presence of added calcium chloride, an initial, fast, first-order reaction represents etherification of the hydroxyl groups on the... 

Mark and Rechnitz [3] systematized a vast amount of experimental material that can be used directly in KGCM. Some data are presented here that show the wide differences in organic compounds with regard to their kinetic characteristics. Table 2.1 [14] gives the relative rates of reaction of olefins with perbenzoic acid and Table 2.2 summarizes the rates of the etherification reaction of carboxylic acids with diphenyldiazomethane [15]. The tabulated data are indicative of large differences in organic compounds as far as their reactivity is concerned. The rates of reaction of some isomers differ so widely that one can, for example, analyse secondary and tertiary alkyl bromides in the presence of primary alkyl bromides in a reaction with silver nitrate [16]. It is possible to differentiate between CIS and trans isomers of 1,3-dienes by their reaction with dienophils (e.g., chloromethylene anhydride) because the cis isomer reacts much more slowly than the trans isomer [17]. 

The pulse chromatographic method was also used to study the kinetics of the etherification of alcohols of various structures with acetic anhydride [74]. The reaction kinetics were studied for high-boiling alcohols the volatile reagent (acetic anhydride) was fed into the rdactor column in the form of a pulse, and the involatile one (alcohol) was present in the column reactor as the stationary phase. Unlike the pulse method used in studying the reactions involved in diene synthesis, in the etherification of an alcohol with acetic anhydride one of the reaction products (acetic acid) is eluted from the column reactor after the starting component (acetic anhydride). The reaction of alcohol etherification was examined at 80—130 C. The mixture of acetic anhydride with the standard (benzene) was pulsed into the reactor column in which the alcohol under study served as the stationary phase. Various extents of reaction were achieved by varying the carrier gas flow-rate. Table 2.6 summarizes the kinetic characteristics of the etherification of alcohols with acetic anhydrides [74]. The rate constants decrease in the order primary > secondary > tertiary. 

KINETIC CHARACTERISTICS OF ETHERIFICATION OF ALCOHOLS WITH ACETIC ANHYDRIDE... 

---