Hydroxy catalyst

Hoesch synthesis A variation of the Gattermann synthesis of hydroxy-aldehydes, this reaction has been widely applied to the synthesis of anthocyanidins. It consists of the condensation of polyhydric phenols with nitriles by the action of hydrochloric acid (with or without ZnCl2 as a catalyst). This gives an iminehydrochloride which on hydrolysis with water gives the hydroxy-ketone. 

Acetaldehyde (and other aldehydes containing at least one hydrogen atom in the a position) when treated with a small quantity of dilute sodium hydr oxide solution or other basic catalyst gives a good yield of aldol (p hydroxy-n-but3Taldehyde) (I), which readily loses water, either by heating the isolated aldol alone or with a trace of mineral acid, to form crotonaldehyde (II) ... 

Basic catalysts other than alkali acetates have been employed in the Perkin reaction thus salicylaldehyde condenses with acetic anhydride in the presence of triethylamine to yield coumarin (tlie lactone of the cis form of o-hydroxy-cinnamio acid) together with some of the acetyl derivative of the trans form (o-acetoxycoumaric acid) ... 

Phenols, unlike amines, cannot be acetylated satisfactorily in aqueous solution acetylation proceeds readily with acetic anhydride in the presence of a little concentrated sulphuric acid as catalyst. Salicylic acid (o-hydroxy-benzoic acid) upon acetylation yields acetylsalicylic acid or aspirin ... 

The first practical method for asymmetric epoxidation of primary and secondary allylic alcohols was developed by K.B. Sharpless in 1980 (T. Katsuki, 1980 K.B. Sharpless, 1983 A, B, 1986 see also D. Hoppe, 1982). Tartaric esters, e.g., DET and DIPT" ( = diethyl and diisopropyl ( + )- or (— )-tartrates), are applied as chiral auxiliaries, titanium tetrakis(2-pro-panolate) as a catalyst and tert-butyl hydroperoxide (= TBHP, Bu OOH) as the oxidant. If the reaction mixture is kept absolutely dry, catalytic amounts of the dialkyl tartrate-titanium(IV) complex are suflicient, which largely facilitates work-up procedures (Y. Gao, 1987). Depending on the tartrate enantiomer used, either one of the 2,3-epoxy alcohols may be obtained with high enantioselectivity. The titanium probably binds to the diol grouping of one tartrate molecule and to the hydroxy groups of the bulky hydroperoxide and of the allylic alcohol... 

In peptide syntheses, where partial racemization of the chiral a-carbon centers is a serious problem, the application of 1-hydroxy-1 H-benzotriazole ( HBT") and DCC has been very successful in increasing yields and decreasing racemization (W. Kdnig, 1970 G.C. Windridge, 1971 H.R. Bosshard, 1973), l-(Acyloxy)-lif-benzotriazoles or l-acyl-17f-benzo-triazole 3-oxides are formed as reactive intermediates. If carboxylic or phosphoric esters are to be formed from the acids and alcohols using DCC, 4-(pyrrolidin-l -yl)pyridine ( PPY A. Hassner, 1978 K.M. Patel, 1979) and HBT are efficient catalysts even with tert-alkyl, choles-teryl, aryl, and other unreactive alcohols as well as with highly bulky or labile acids. 

The 4-hydroxy-1-alkene (homoallylic alcohol) 81 is oxidized to the hetni-acetal 82 of the aldehyde by the participation of the OH group when there is a substituent at C3. In the absence of the substituent, a ketone is obtained. The hemiacetal is converted into butyrolactone 83[117], When Pd nitro complex is used as a catalyst in /-BuOH under oxygen, acetals are obtained from homoallylic alcohols even in the absence of a substituent at C-3[l 18], /-Allylamine is oxidized to the acetal 84 of the aldehyde selectively by participation of the amino group[l 19],... 

The rt,/3-unsaturated linear carbonyl compound 39 is obtained by the decomposition of the cyclic hydroperoxide 38 with PdCl2,[35]. The a, 0-epoxy ketone 40 is isomerized to the /3-diketone 41 with Pd(0) catalyst[36]. The 1,4-epiperoxide 42 is converted into the /3-hydroxy ketone 43 and other products[37]. 

Hydroxy-2-methylpropanenitrile is then reacted with methanol (or other alcohol) to yield methacrylate ester. Free-radical polymerization is initiated by peroxide or azo catalysts and produce poly(methyl methacrylate) resins having the following formula ... 

Hexamethylolmelamine can further condense in the presence of an acid catalyst ether linkages can also form (see Urea Eormaldehyde ). A wide variety of resins can be obtained by careful selection of pH, reaction temperature, reactant ratio, amino monomer, and extent of condensation. Eiquid coating resins are prepared by reacting methanol or butanol with the initial methylolated products. These can be used to produce hard, solvent-resistant coatings by heating with a variety of hydroxy, carboxyl, and amide functional polymers to produce a cross-linked film. 

Noncatalytic Reactions Chemical kinetic methods are not as common for the quantitative analysis of analytes in noncatalytic reactions. Because they lack the enhancement of reaction rate obtained when using a catalyst, noncatalytic methods generally are not used for the determination of analytes at low concentrations. Noncatalytic methods for analyzing inorganic analytes are usually based on a com-plexation reaction. One example was outlined in Example 13.4, in which the concentration of aluminum in serum was determined by the initial rate of formation of its complex with 2-hydroxy-1-naphthaldehyde p-methoxybenzoyl-hydrazone. ° The greatest number of noncatalytic methods, however, are for the quantitative analysis of organic analytes. For example, the insecticide methyl parathion has been determined by measuring its rate of hydrolysis in alkaline solutions. 

Polymer-based rocket propellants are generally referred to as composite propellants, and often identified by the elastomer used, eg, urethane propellants or carboxy- (CTPB) or hydroxy- (HTPB) terrninated polybutadiene propellants. The cross-linked polymers act as a viscoelastic matrix to provide mechanical strength, and as a fuel to react with the oxidizers present. Ammonium perchlorate and ammonium nitrate are the most common oxidizers used nitramines such as HMX or RDX may be added to react with the fuels and increase the impulse produced. Many other substances may be added including metallic fuels, plasticizers, stabilizers, catalysts, ballistic modifiers, and bonding agents. Typical components are Hsted in Table 1. 

P-Hydroxy acids lose water, especially in the presence of an acid catalyst, to give a,P-unsaturated acids, and frequendy P,y-unsaturated acids. P-Hydroxy acids do not form lactones readily because of the difficulty of four-membered ring formation. The simplest P-lactone, P-propiolactone, can be made from ketene and formaldehyde in the presence of methyl borate but not from P-hydroxypropionic acid. P-Propiolactone [57-57-8] is a usehil intermediate for organic synthesis but caution should be exercised when handling this lactone because it is a known carcinogen. 

Biacetyl is produced by the dehydrogenation of 2,3-butanediol with a copper catalyst (290,291). Prior to the availabiUty of 2,3-butanediol, biacetyl was prepared by the nitrosation of methyl ethyl ketone and the hydrolysis of the resultant oxime. Other commercial routes include passing vinylacetylene into a solution of mercuric sulfate in sulfuric acid and decomposing the insoluble product with dilute hydrochloric acid (292), by the reaction of acetal with formaldehyde (293), by the acid-cataly2ed condensation of 1-hydroxyacetone with formaldehyde (294), and by fermentation of lactic acid bacterium (295—297). Acetoin [513-86-0] (3-hydroxy-2-butanone) is also coproduced in lactic acid fermentation. 

Functional Monomers. Hydroxy functional methacrylates ate accessible by the reaction of methacryhc acid and ethylene oxide or ptopjiene oxide in the presence of chromium (61), iron (62), or ion-exchange catalysts (63). 

H-acid, l-hydroxy-3,6,8-ttisulfonic acid, which is one of the most important letter acids, is prepared as naphthalene is sulfonated with sulfuric acid to ttisulfonic acid. The product is then nitrated and neutralized with lime to produce the calcium salt of l-nitronaphthalene-3,6,8-ttisulfonic acid, which is then reduced to T-acid (Koch acid) with Fe and HCl modem processes use continuous catalytical hydrogenation with Ni catalyst. Hydrogenation has been performed in aqueous medium in the presence of Raney nickel or Raney Ni—Fe catalyst with a low catalyst consumption and better yield (51). Fusion of the T-acid with sodium hydroxide and neutralization with sulfuric acid yields H-acid. Azo dyes such as Direct Blue 15 [2429-74-5] (17) and Acid... 

Hydrogen Sulfide andMercaptans. Hydrogen sulfide and propylene oxide react to produce l-mercapto-2-propanol and bis(2-hydroxypropyl) sulfide (69,70). Reaction of the epoxide with mercaptans yields 1-aLkylthio- or l-arylthio-2-propanol when basic catalysis is used (71). Acid catalysts produce a mixture of primary and secondary hydroxy products, but ia low yield (72). Suitable catalysts iaclude sodium hydroxide, sodium salts of the mercaptan, tetraaLkylammonium hydroxide, acidic 2eohtes, and sodium salts of an alkoxylated alcohol or mercaptan (26,69,70,73,74). 

The reaction is of practical importance in the vulcanization of siUcone mbbers (see Rubber compounding). Linear hydroxy-terrninated polydimethyl siloxanes are conveniently cross-linked by reaction with methyldiethoxysilane or triethoxysilane [998-30-1]. Catalysts are amines, carboxyflc acid salts of divalent metals such as Zn, Sn, Pb, Fe, Ba, and Ca, and organotin compounds. Hydroxy-terrninated polysiloxanes react with Si—H-containing polysiloxanes to... 

Other methods include ring opening of parasorbic acid [108-54-3] (5-lactone of 5-hydroxy-2-hexenoic acid) in hydrochloric acid or in alkaline solutions (43,44), the ring opening of y-vinyl- y-butyrolactone in various catalysts (45,46), or isomerization of 2,5-hexadienoic acid esters (47,48). Other methods are described in thehterature (6,49,50). 

Hydroxy group containing tertiary amines are also used because they become incorporated into the polymer stmcture, which eliminates odor formation ia the foam (3). Delayed-action or heat-activated catalysts are of particular interest ia molded foam appHcations. These catalysts show low activity at room temperature but become active when the exotherm builds up. In addition to the phenol salt of DBU (4), benzoic acid salts of Dabco are also used (5). 

The avermectins also possess a number of aUyflc positions that are susceptible to oxidative modification. In particular the 8a-methylene group, which is both aUyflc and alpha to an ether oxygen, is susceptible to radical oxidation. The primary product is the 8a-hydroperoxide, which has been isolated occasionally as an impurity of an avermectin B reaction (such as the catalytic hydrogenation of avermectin B with Wilkinson s rhodium chloride-triphenylphosphine catalyst to obtain ivermectin). An 8a-hydroxy derivative can also be detected occasionally as a metaboUte (42) or as an impurity arising presumably by air oxidation. An 8a-oxo-derivative can be obtained by oxidizing 5-0-protected avermectins with pyridinium dichromate (43). This also can arise by treating the 8a-hydroperoxide with base. 

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