Etherification in Stages

Due to the high reaction temperatures required during the last stages of these syntheses, side reactions cannot be avoided. Acetaldehyde, carboxyl endgroups, and vinyl endgroups are formed during PET and PEN synthesis. The formation of 2,2/-oxydiethylene moieties in polymer chains by etherification of hydroxyl endgroups is also a well-known side reaction of EG polyester syntheses.264 These reactions should be carefully controlled since they can exert an important influence on polymer properties such as Ts, mechanical properties, hydrolytic stability, and discoloration. 

The etherification stage entails only the substitution of chlorine atoms which are situated directly at the silicon atom, forming methyl(chloromethyl)diethoxysilane (the chlorine in the chloromethyl radical is not affected) ... 

Diethylaminomethyltriethoxysilane (ADE-3) is synthesised in two stages. At the first stage, the etherification of chloromethyltrichlorosilane with anhydrous ethyl alcohol forms chloromethyltriethoxysilane. 

The second stage, the re-etherification of chloromethyltriethoxysilane with triethanolamine, is actually a process of ester condensation since the ester group of triethanolamine has a low carbonyl activity, one should employ strong bases, e.g. alcoholates of alkali metals, as the condensing agent. Consequently, re-etherification can be generalised in the following way ... 

The hydrolytic condensation of phenylethoxysilanes is carried out in butyl alcohol that is why at this stage we observe a partial re-etherification of phenylethoxysilanes with butyl alcohol and partial condensation of the re-etherification products. Generally, the process can be described by the following scheme ... 

Below let us use poly [4-[2-(hydroxyphenyl)propyl-2]-phenyl]phenyl siloxane as an example and illustrate the production of polyphenylsiloxanes from trialkoxyphenylsilane (in our case tributoxy-phenylsilane) synthesised by the second technique, the etherification of phenyltrichlorosilane. The production comprises the following main stages the synthesis of tributoxyphenylsilane and its partial hydrolytic condensation the re-etherification of polybutoxyphenylsiloxane with diphenylolpropane. 

When the temperature in reactor 8 is 135 °C and the distillation of butyl alcohol stops, the temperature is raised further (to 145-160 °C) at a residual pressure of 330-200 GPa. In these conditions re-etherification is accompanied by further condensation of the polymer. The apparatus is periodically sampled to check the degree of polymer condensation by the gelatinisation time at 250 °C before stage C. If the time does not exceed 6 minutes, condensation is considered finished (the given polymerisation degree is attained). The supply of vapour into the jacket is immediately stopped and the hot polymer is loaded off. 

Etherification of propylene and isopropyl alcohol to produce diisopropyl ether, an octane enhancer, has been patented as a two-stage process.The first step involves the hydration of propylene to isopropyl alcohol using acidic ion-exchange resins or acidic zeolites and an optional cosolvent and the second step involves the etherification of propylene and isopropyl alcohol using an acidic catalyst such as Amberlyst 36 in a CD column. 

To provide an illustration, the flow sheet of the IFP process shown in Fig. 3.12 comprises two possible variants. The simpler corresponds to the direct use of the etherified solution in the gasoline pool, withont separating the excess inethanol contained. Operations are conducted with two reactors in series the first with an upflow stream and expanded bed with recycle of part of the previously cooled effluent for better control of the temperature rise, and the second with a downflow stream and a fixed bed The more complex involves the recovery of excess methanol, first by azeotropic distillation in a depentanizer with part of the unconvened hydrocarbons, and then by water washing of this raffinate. The hydrocarbon phase is added to the bottom of the depentanizer. The water/methanol mixture is distilled to recover and recycle the alcohol to the etherification stage. 

The use of RD in the manufacture of other ethers such as ETBE, TAME, and so on, has been demonstrated to be beneficial and several patents and investigations have emerged [3, 4]. UOP describes a process for the manufacture of DIPE (di-isopropyl ether), which uses propylene and water feedstock. It is a two-stage RD process associated with simultaneous hydration and etherification [5]. The ethers, being the heaviest components, are collected in the bottom stream. 

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