Zinc chloride, acetonation catalyst with

Diols yield acetonides, even in the presence of a 17oc-hydroxylgroup. Reaction with acetone in the presence of zinc chloride as catalyst leads to the formation of diacetone alcohol acetal as a by-product. ... 

Acetic acid, as acetonation catalyst with zinc chloride, III, 51 glacial, for laboratory crystallization of /3-glucopyranose, V, 136 as intermediate in fat formation, II,... 

One of the best-known isopropylidene derivatives is diacetone glucose (1,2 5,6-di-O-isopropylidene D-glucofuranoside). It is prepared by the reaction of D-glu-cose in anhydrous acetone at 20°C with sulfuric acid or zinc chloride as catalysts [21] (reaction 4.20). The reaction of acetone has a preference for a cw-vicinal diol. 

Practical interest in high-molecular-weight poly (propylene oxide) centers in its potential use as an elastomer (19). Copolymerization of propylene oxide with allyl glycidyl ether gives a copolymer with double bonds suitable for sulfur vulcanization. Table IV shows the properties of elastomers made with a copolymer prepared with a zinc hexacyano-ferrate-acetone-zinc chloride complex. Also shown are the properties of elastomers made from partially crystalline copolymers prepared with zinc diethyl-water catalyst. Of particular interest are the lower room-... 

It has been claimed that acetalation of25 with acetone-sulfuric acid (or other dehydrating agent) in the presence of ultrasonic waves lessens the time of reaction (to <70 min), and 26 may be isolated in 76% yield.109 In addition, several reports have been published on the use of other acid catalysts, namely, zinc chloride-phosphoric acid,110... 

The stability of an acetal or a ketal may depend on the catalyst employed in its synthesis. For this and other reasons, Fischer and Taube20 recommended the use of zinc chloride, rather than a mineral acid, as the catalyst in acetonation processes. Presumably the instability of the products prepared with the aid of strong acids is due to the difficulty of ensuring complete removal of the catalysts. 

Further evidence for the hypothesis was found in the patent describing the isoprene—acrylonitrile—zinc chloride system (23). On adding a four-fold excess of isoprene to an equimolar mixture of acrylonitrile and zinc chloride, in the absence of a free radical catalyst, an exothermic reaction occurs after approximately 30 minutes. The recovered polymer is insoluble in hydrocarbons, chloroform, and acetone. This eliminates polyisoprene and the alternating copolymer. The yield of product is 12%, calculated a polyacrylonitrile, compared with the 16.8% yield of copolymer obtained when excess acrylonitrile and a free radical catalyst are used. 

Halide exchange, sometimes call the Finkelstein reaction, is an equilibrium process, but it is often possible to shift the equilibrium. The reaction is most often applied to the preparation of iodides and fluorides. Iodides can be prepared from chlorides or bromides by taking advantage of the fact that sodium iodide, but not the bromide or chloride, is soluble in acetone. When an alkyl chloride or bromide is treated with a solution of sodium iodide in acetone, the equilibrium is shifted by the precipitation of sodium chloride or bromide. Since the mechanism is Sn2, the reaction is much more successful for primary halides than for secondary or tertiary halides sodium iodide in acetone can be used as a test for primary bromides or chlorides. Tertiary chlorides can be converted to iodides by treatment with excess Nal in CS2, with ZnCl2 as catalyst. Vinylic bromides give vinyhc iodides with retention of configuration when treated with KI and a nickel bromide-zinc cata-lyst, ° or with KI and Cul in hot HMPA. ° °... 

The condensation of acetone with D-ribose, with sulfuric acid as the catalyst, has also been examined in detail.17 The major component is 2,3-O-isopropylidene-D-ribofuranose (59%), together with three minor components l,5-anhydro-2,3-0-isopropylidene-D-ribofuranose (9%), 1,2 3,4-di-O-isopropylidene-a-D-ribopyranose (3%), and 1,2-0-isopropylidene-a-D-ribofuranose (6%). The authors observed that the only marked difference when other catalysts (such as copper sulfate or zinc chloride) were used was the absence of the anhydro compounds. Assuming that the 1-hydroxyl group is equatorial, the preponderance of the 2,3-acetal is consistent with the thermodynamic stability of the isomer having the least number of endo substituents and with the unfavorable interactions between the acetal rings in the 1,2 3,4-diacetal, which possesses a cis-syn-cis arrangement of rings.10... 

It should be emphasized that, in order to make an assessment of the stereochemical principles involved in the formation of cyclic acetals of aldoses and aldosides, the reaction products from a given condensation must be analyzed quantitatively, and the structures of the products determined. In addition, the reaction should, ideally, have reached equilibrium under truly reversible conditions. It now seems that the interpretation of some of the previous results must be carefully reconsidered. The valuable investigations of Buchanan and Saunders have revealed the possibility that condensations catalyzed by zinc chloride may not proceed in a truly reversible manner. Dorcheus and Williams also remarked that the catalytic action of zinc chloride will be lost through formation of the hydrated complex, ZnCU (H80)2. This change will result in kinetic control of the reaction. It has been found, for example, that reaction of methyl a-D-altropyranoside (13) with acetone and sulfuric acid affords a 42% yield of the 3,4-0-isopropylidene acetal. Using zinc chloride as the catalyst, both the 3,4- and the 4,6-0-isopropylidene acetal are obtained. Similar results were re-... 

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. 

Isopropylidene derivatives of carbohydrates (acetone sugars)915b are obtained from sugars or suitable derivatives by treatment with much acetone in the presence of a catalyst such as an acid, zinc chloride, or anhydrous copper sulfate. It helps further to add a water-binding material such as sodium sulfate. 

Ohle and Koller, Slobodin and Klimov, Bell, and Brady showed that low concentrations ( 0.5%) of sulfuric acid as catalyst for 1-3 days at room temperature lead to the formation of 1. Slightly higher concentrations of catalyst and shorter reaction times (3-24 hours) favor an increase in the proportion of 2, and lead to the isolation of mixtures of diacetals 1 and 2. However, at high concentrations of acid ( 4%), or after prolonged reaction, compound 2 was found to be the preponderant product. Evidently (see also Section III,2 p. 218), the diacetal 1 is the product of kinetically controlled condensation of D-fructose with acetone, but it rearranges, at a rate proportional to the concentration of the sulfuric acid catalyst, to the diacetal 2, which is thermodynamically more stable than 1, and thus preponderates at equilibrium. The use of zinc chloride as the catalyst is known to favor the formation of 1. 

PANIC at 250 MHz, has shown that it is the 1 3 2 6-triacetal and not the 1,2 3,5 A 6-trlacetal as previously claimed. The three products from acetalatlon of D-mannitol with 2-methoxypropene in DMF with tosic acid catalyst have been shown to be 1,2 5,6- 1 2 4 6- and 1,2 3,6-di-0-isopropylidene-D-mannitol. The preparation of 1 2 5,6-di-O-isopropylidene-D-mannitol by three alternative procedures for acetonation of D-mannitol has been investigated using acetylation and capillary g.l.c. to monitor the products. The highest yield was obtained by propanone-zinc chloride, whereas 2 2-dlmethoxypropane -tin(II) chloride and 2-methoxypropene - tosic acid gave more complex mixtures contrary to claims in the literature. A new trlacetal 1 2 3,6 4,5-trl-O-lsopropylidene-D-mannltol vas Isolated and its graded hydrolysis compared with that of 1 2 3 4 5 6-trlacetal. Acetal-... 

Condensation of 2-mercaptoethanol or 3-mercaptopropanoI with ketones is usually achieved with the aid of an acid catalyst. Hydrogen chloride has been used but more common agents are boron trifluoride , freshly fused zinc chloride or p-toluenesulphonic acid . An exchange method between 2,2-dimethyl-1,3-oxathiolane or 2,2-dimethyl-1,3-oxathiane and a non-volatile ketone leads to formation of the new mono-thioacetal and acetone . The equilibrium is displaced by continuous distillation of the acetone formed (equation 71). With saturated ketones, mostly steroids, the yields of the above methods are comparable and are usually in the 60-90% range. With a,j3-unsaturated ketones, the yields were significantly lower . 

A second enzymatic site, which has been selected as a target to direct the chelating potential of the thiosemicarbazone molecule, is pyiidoxal phospho-kinase [65]. This catalyst is a zinc-requiring enzyme [66] that catalyzes the phosphorylation of pyridoxine at position 5 to form the active coenzyme form. In an effort to accomplish inhibition, 2-formyl-3-hydroxy-4,5-bis(hydroxy-methyOpyridine thiosemicarbazone (117) was synthesized [65]. This was accomplished by two different procedures. The common intermediate, 3-acetoxy-2,4,5-tris(acetoxymethyl)pyridine (111) [67], upon acid hydrolysis afforded 3-hydroxy-2,4,5-tris(hydroxymethyl)pyridine hydrochloride (112), which was treated with hydrogen chloride as a suspension in acetone [68). The amount of hydrogen chloride taken up by the suspension is a critical factor and. 

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