Zinc sulfuric acid, hydrogenation catalyst

The condensation of a carbonyl compound with a polyhydric alcohol, to form a cyclic acetal, proceeds readily under anhydrous conditions in the presence of a catalyst, for example, concentrated sulfuric acid, hydrogen chloride, or anhydrous zinc chloride. The reaction involves the attack of the carbonium ion (1) on the alcoholic oxygen atom. The hemiacetal thus formed is rarely stable, and ring closure follows (see p. 302). 

Aluminium chloride, zinc chloride, sulfuric acid, hydrogen chloride, etc., may act as the catalyst. 

Catalysts zinc chloride, sulfuric acid, hydrogen chloride, etc. 

The synthesis of 2,4-dihydroxyacetophenone [89-84-9] (21) by acylation reactions of resorcinol has been extensively studied. The reaction is performed using acetic anhydride (104), acetyl chloride (105), or acetic acid (106). The esterification of resorcinol by acetic anhydride followed by the isomerization of the diacetate intermediate has also been described in the presence of zinc chloride (107). Alkylation of resorcinol can be carried out using ethers (108), olefins (109), or alcohols (110). The catalysts which are generally used include sulfuric acid, phosphoric and polyphosphoric acids, acidic resins, or aluminum and iron derivatives. 2-Chlororesorcinol [6201-65-1] (22) is obtained by a sulfonation—chloration—desulfonation technique (111). 1,2,4-Trihydroxybenzene [533-73-3] (23) is obtained by hydroxylation of resorcinol using hydrogen peroxide (112) or peracids (113). 

Tetrahydropyrane has been prepared by hydrogenation of dihydropyrane using a platinum black catalyst 1 by heating pen-tamethylene bromide with water 2 3 or with water and zinc oxide in a sealed tube 4 or by heating pentamethylene glycol with three volumes of 60 per cent sulfuric acid in a pressure tube.5... 

The reactions are carried out at about 900 to 1,000°C and catalyzed by nickel, nickel-alumina, or rhodium-alimina catalysts. In the laboratory, hydrogen may be prepared by the reaction of zinc or iron with dilute hydrochloric or sulfuric acid ... 

In this section, consideration will be given to the actual processes of acetal- or ketal-formation and not to the more indirect methods by which acetals and ketals of the polyhydric alcohols may be synthesized from compounds (e.g. derivatives of the monosaccharides) containing preformed alkylidene or arylidene groupings. The condensation of a carbonyl compound with a glycol is facilitated by acidic catalysts, and, since the reaction is reversible, by dehydration. The catalysts most frequently employed are concentrated sulfuric, hydrochloric and hydro-bromic acids, gaseous hydrogen chloride, zinc chloride and cupric sulfate others are phosphorus pentoxide, sulfosalicylic acid, and anhydrous sodium sulfate. The formation of benzylidene compounds is promoted less efficiently by phosphorus pentoxide than by either concentrated sulfuric acid or concentrated hydrochloric acid 1" the reaction is assisted by chloro- and nitro-substituents on the aromatic nucleus, but hindered by methyl- and methoxy-groups.18... 

Methanation as final purification for the raw gas from partial oxidation was proposed by Topsoe [739]. In this case the shift conversion is carried out in two stages with a special sulfur-tolerant shift catalyst followed by removal of hydrogen sulfide and carbon dioxide in an acid gas removal unit. Because of the potential danger of a sulfur break-through causing poisoning, the normal copper - zinc - alumina catalyst is usually not applied, which is surprising as the same risk exists in partial oxidation based methanol plants for the similarly composed methanol catalyst. 

The chiral amino thioester 9, a thioester analog of DBNE, does not form a zinc amide or a zinc thioate because it does not possess an acidic hydrogen atom. Simple coordination of nitrogen and sulfur atoms to the zinc atom of diethylzinc may generate an efficient chiral catalyst. 

D-Glucose and acetone, with a wide variety of catalysts, for example, 1-2% hydrogen chloride, zinc chloride and 85% phosphoric acid, anhydrous copper(II) sulfate, concentrated sulfuric acid, cation-exchange resins, or the ethyl ester of metaphosphoric acid, react to give 1,2 5,6-di-O-isopropylidene-a-D-glucofuranose (24). A comprehensive survey of the evidence, and confirmation of the furanose structure of the diacetal (24) was provided by Anderson, Charlton, and Haworth, nearly 30 years after the initial preparation of the diacetal. The diacetal has been used extensively for the preparation of C-3 substituted D-glucose derivatives and 3-a- and 3- 3-linked disaccharides. 

Alkylation of Aromatics. Aromatic hydrocarbons containing a replaceable hydrogen can be alkylated unless steric effects prevent introduction of the alkyl group (61,78-82). The reaction is called the Friedel-Crafts alkylation, first realized in the presence of aluminum chloride, which is the catalyst still the most frequently used and studied in Friedel-Crafts reactions. In addition, many other acid catalysts are effective (80,82-84). These include other Lewis acids (other aluminum halides, gallium chloride, boron trifluoride, ferric chloride, zinc chloride, stannous and stannic chloride, antimony chloride) and protic acids (hydrogen fluoride, concentrated sulfuric acid, phosphoric acid, polyphosphoric acid, trifluo-romethanesulfonic acid, and alkane- and arenesulfonic acids). 

Metal oxides, sulfides, and hydrides form a transition between acid/base and metal catalysts. They catalyze hydrogenation/dehydro-genation as well as many of the reactions catalyzed by acids, such as cracking and isomerization. Their oxidation activity is related to the possibility of two valence states which allow oxygen to be released and reabsorbed alternately. Common examples are oxides of cobalt, iron, zinc, and chromium and hydrides of precious metals that can release hydrogen readily. Sulfide catalysts are more resistant than metals to the formation of coke deposits and to poisoning by sulfur compounds their main application is in hydrodesulfurization. 

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