Conventional dilute acid-catalyzed

Unsubstituted 20-ketones undergo exchange dioxolanation nearly with the same ease as saturated 3-ketones although preferential ketalization at C-3 can be achieved under these conditions. " 20,20-Cycloethylenedioxy derivatives are readily prepared by acid-catalyzed reaction with ethylene glycol. The presence of a 12-ketone inhibits formation of 20-ketals. Selective removal of 20-ketals in the presence of a 3-ketal is effected with boron trifluoride at room temperature. Hemithioketals and thioketals " are obtained by conventional procedures. However, the 20-thioketal does not form under mild conditions (dilution technique). ... 

The 2-butanol feedstock is conventionally obtained by the sulfuric acid-catalyzed addition of water to -butenes. This is a two-step reaction involving sulfation and hydrolysis in which the conversion of -butenes is 90% and selectivity to 2-butanol is 95% (15). During operation the sulfuric acid becomes diluted and must be reconcentrated before reuse. In 1983 Deutsche Texaco commercialized a single-step route in which 2-butanol is formed by the hydration of -butenes in the presence of a strongly acidic ion-exchange resin containing sulfonic acid groups (16—18). The direct reaction is carried out at 150—160°C and 7 MPa. Virtually anhydrous 2-butanol is recovered in this process (19). Direct hydration requires lower utilities and investment costs, operates at 99% selectivity to 2-butanol, but is hindered by low (5—15%) -butene conversion per pass. 

In the conventional dilute sulfuric acid-catalyzed percolation process, the plant raw material containing pentosans is mixed with dilute sulfuric acid and, in the first step, pentosans are hydrolyzed to pentoses (C6Hio05)n, which are then cyclodehydrated to furfural in the second step. The frirfiirai formed is recovered by steam distillation and fractionation. The chemical reaction is shown in Figure I. The mechanism of the reaction (4) is shown in Figure 2. 

IR spectra of xerogels prepared by a single-step acid-catalyzed hydrolysis of TEOS (r = 50) followed by drying at 40 C or heat treatments in air at temperatures ranging from 250 to 800 C. Shown for comparison are the spectra of the TEOS precursor and conventional u-SiOj. The samples are diluted in a nujol emulsion, and bands due to the nujol are indicated by dots [35]. 

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