Etherification catalyst

The ion-exchange resins used as etherification catalysts are strongly acidic cation-exchange resins. These materials consist typically of polystyrene chains that have been linked with divinylbenzene (DVB), the amount of which determines the degree of crosslinking and regulates the rigidity of the structure schematically presented in Fig. 10.3 [24],... 

Undesirable side reactions often occur when concentrated sulfuric acid is used. For sensitive substances it is thus advisable to use an organic sulfonic acid such as / -toluenesulfonic acid as etherification catalyst.664 For example, ethers of cyclic enols665, 666 can be obtained by boiling the reactants with a little /7-toluenesulfonic acid in benzene while removing the resulting water in a continuous water-separator. 

Sulfonic acid groups as active sites well known active etherification catalyst... 

Etherification catalysts include mineral acids such as sulfuric and perchloric acid, but these tend to provide double the amounts of dehydration products compared with other catalysts. Lewis acids such as boron trifluoride and iron (Ill)-exchanged montmorillonite clays are also effective at catalyzing these reactions. Boron trifluoride provides the most consistent yields increases in catalyst concentration generally increase ether yields and/or reduce reaction times. Iron (III) clays provided high... 

Isomerization. Isomerization is a catalytic process which converts normal paraffins to isoparaffins. The feed is usually light virgin naphtha and the catalyst platinum on an alumina or zeoflte base. Octanes may be increased by over 30 numbers when normal pentane and normal hexane are isomerized. Another beneficial reaction that occurs is that any benzene in the feed is converted to cyclohexane. Although isomerization produces high quahty blendstocks, it is also used to produce feeds for alkylation and etherification processes. Normal butane, which is generally in excess in the refinery slate because of RVP concerns, can be isomerized and then converted to alkylate or to methyl tert-huty ether (MTBE) with a small increase in octane and a large decrease in RVP. 

Etherification. Isopropyl alcohol can be dehydrated ia either the Hquid phase over acidic catalysts, eg, sulfuric acid, or ia the vapor phase over acidic aluminas to give diisopropyl ether (DIPE) and propylene (qv). 

Reaction of olefin oxides (epoxides) to produce poly(oxyalkylene) ether derivatives is the etherification of polyols of greatest commercial importance. Epoxides used include ethylene oxide, propylene oxide, and epichl orohydrin. The products of oxyalkylation have the same number of hydroxyl groups per mole as the starting polyol. Examples include the poly(oxypropylene) ethers of sorbitol (130) and lactitol (131), usually formed in the presence of an alkaline catalyst such as potassium hydroxide. Reaction of epichl orohydrin and isosorbide leads to the bisglycidyl ether (132). A polysubstituted carboxyethyl ether of mannitol has been obtained by the interaction of mannitol with acrylonitrile followed by hydrolysis of the intermediate cyanoethyl ether (133). 

Methyl tert-Butyl Ether (MTBE). Methyl tert-hutyi ether [1634-04-4] is made by the etherification of isobutylane with methanol, and there are six commercially proven technologies available. These technologies have been developed by Arco, IFF, CDTECH, Phillips, Snamprogetti, and Hbls (hcensed jointly with UOP). The catalyst in all cases is an acidic ion-exchange resin. The United States has been showing considerable interest in this product. Western Europe has been manufacturing it since 1973 (ANIC in Italy and Huls in Germany). Production of MTBE in Western Europe exceeded 600,000 tons in 1990. 

Several derivatives of cellulose, including cellulose acetate, can be prepared in solution in dimethylacetamide—lithium chloride (65). Reportedly, this combination does not react with the hydroxy groups, thus leaving them free for esterification or etherification reactions. In another homogeneous-solution method, cellulose is treated with dinitrogen tetroxide in DMF to form the soluble cellulose nitrite ester this is then ester-interchanged with acetic anhydride (66). With pyridine as the catalyst, this method yields cellulose acetate with DS < 2.0. 

Catalyst-resin heads placed in cloth hags attached to Etherifications Smith et al., U.S. Patent 4,443,559 (1981)... 

Modification of urea-formaldehyde resins with other reagents gives rise to a number of useful materials. For example, co-condensation of urea-formaldehyde and a monohydric alcohol in the presence of small quantities of an acidic catalyst will involve simultaneous etherification and resinification. n-Propanol, n-butanol and isobutanol are commonly used for this purpose. As an example n-butanol will react with the methylol urea as shown in Figure 24.4. 

Commercial alkylation is the reaction of isobutane with C3 through Cg olefins in the presence of either sulfuric acid or hydrofluoric acid (see Example 10-1). Etherification is the reaction of a tertiary olefin with an alcohol or water in the presence of an acidic catalyst (see Example 10-2). 

Ferrocenylacetonitrjle, 40, 46 Fluoboric acid as catalyst for diazomethane etherifications, 41, 9, 10 9-Fluobenone, 2,4,5,7-tetranitro-, 42,95... 

Tanabe and Hdlderich (1999) have given an extensive statistical survey of industrial processes using solid acids/bases as catalysts. Over 300 solids and bases have been covered. A variety of reactions like alkylation, isomerization, amination, cracking, and etherification with catalysts like zeolites, oxides, complex oxides, phosphates and ion-exchange resins have been covered. Over 120 industrial processes are referred with 180 different catalysts. 

A number of examples have been cited by Chakrabarti and Sharma (1993) and Sharma (1995). The example of etherification of phenols, substituted phenols, cresols, naphthols, etc., with isobutylene and isoamylene may be empahsized where homogeneous catalysts lead to... 

Clay-supported heteropoly acids such as H3PW12O40 are more active and selective heterogeneous catalysts for the synthesis of MTBE from methanol and tert-butanol, etherification of phenethyl alcohols with alkanols, and alkylation of hydroquinone with MTBE and tert-butanoi (Yadav and Kirthivasan, 1995 Yadav and Bokade, 1996 Yadav and Doshi, 2000), and synthesis of bisphenol-A (Yadav and Kirthivasan, 1997). 

The etherification between alcohol 10 and imidate 67 was one of the key transformations in the successful preparation of compound 1. The use of HBF4 as the catalyst for the etherification was crucial for obtaining high levels of diastereose-lectivity and relatively high conversion to the desired product 18. The fact that sec-sec ethers have rarely, if ever, been obtained with high levels of diastereocontrol in Sn2 fashion under typical SN1 reaction conditions prompted us to investigate the complex mechanistic details of this exceptional reaction. 

In an effort to identify the origin of the formation of the minor diastereomer 19 and understand whether its formation was a function of a breakdown in the SN2 pathway leading to an SN1 pathway, the activation of the chiral imidate 67 was next investigated. In the etherification reaction between 10 and 67, the acid catalyst increases the electrophilicity of imidate 67 through coordination between the acid... 

In 1978 and 1980 the coupling of aryl bromides and iodides with both aliphatic and aromatic thiols was first reported in the presence of NaO-t-Bu and Pd(PPh3)4 (Equation (35)).118,119 In contrast to aryl halide aminations and etherifications, the thiation reactions did not require unusual catalysts. Yet, reactions that form aryl alkyl sulfides from alkyl thiols occurred in modest yields in many cases ... 

---