Hydrolysis media

Precursors useful in the surface sol-gel process are not restricted to alkoxides. The requirements as precursors are chemisorption on surface hydroxyl groups and regeneration of the hydroxyl groups after hydrolysis. For example, TiO(acac)2 repeatedly adsorbs, when acid and alkali are added to the adsorption and hydrolysis media, respectively. Except for the case of Nb(0"Bu)5, all the compounds listed in Table 6.1 show linear frequency shifts. Adsorption conditions such as concentration, temperature, and immersion time are dependent on the solubility, reactivity, and the ease of hydrolysis of alkoxides. These conditions are varied as the structure of alkoxide units is changed. For example, Ti(01Pr)4, which exists as a monomer in solution [17], requires conditions different from Ti(0"Bu)4, which tends to form oligomer species. 

The rate of hydrolysis depends upon the solubUity of the acetal m the hydrolysis medium. Acetals of low molecular weight are completely hydrolysed by refluxing for 5-10 minutes those of higher molecular weight, and therefore of small solubility, may require 30-60 minutes, but... 

It is frequently advisable in the routine examination of an ester, and before any derivatives are considered, to determine the saponification equivalent of the ester. In order to ensure that complete hydrolysis takes place in a comparatively short time, the quantitative saponi fication is conducted with a standardised alcoholic solution of caustic alkali—preferably potassium hydroxide since the potassium salts of organic acids are usuaUy more soluble than the sodium salts. A knowledge of the b.p. and the saponification equivalent of the unknown ester would provide the basis for a fairly accurate approximation of the size of the ester molecule. It must, however, be borne in mind that certain structures may effect the values of the equivalent thus aliphatic halo genated esters may consume alkali because of hydrolysis of part of the halogen during the determination, nitro esters may be reduced by the alkaline hydrolysis medium, etc. 

Substituted amides suffer hydrolysis with greater difficulty. The choice of an acid or an alkaline medium vill depend upon (a) the solubility of the compound in the medium and (b) the effect of the reagent upon the products of hydrolysis. Substituted amides of comparatively low molecular weight (e.g., acetanilide) may be hydrolysed by boiling either with 10 per cent, sodium hydroxide solution or with 10 per cent, sulphuric acid for 2-3 hours. Other substituted amides are so insoluble in water that little reaction occurs when they are refluxed with dilute acid or dilute alkali for several hours. These include such substances as benzanilide (C(H(CONHC,Hg) and the benzoyl derivative of a naphthylamine (C.HjCONHCioH,) or a toluidine (C gCONHCjH,). For these substances satisfactory results may be obtained with 70 per cent, sulphuric acid this hydrolysis medium is a much better solvent for the substituted amide than is water or more dilute acid it also permits a higher reaction temperature (compare Section IV 192) ... 

We hydrolyzed ATP and ADP in 1 N and 0.1 N HC1 and in buffered solutions at pH 4j nd 8 in which the hydrolysis medium was variously enriched in °0 to either 10% or 20%. To assess the isotopic enrichment of each such solution for use in the nucleotide hydrolysis experiments, we hydrolyzed PCI, in the solution, esterified the resultant phosphoric acid/inorganic phosphate (P.) by reaction with diazomethane, and determined the isotopic distribution of the trimethyl phosphate (TMPO) by mass spectrometry. The 1 N and 0.1 N HC1 hydrolyses were allowed to proceed for 45 min and 10 hr, respectively, at 70, insuring complete conversion of ATP into AMP + 2P. The pH 8 hydrolyses were allowed to proceed for 36 hr at 70 to a point (20-25% completion) at which the ratio of ADP to AMP established that 96% and 4%, respectively, of the P. released had arisen by the primary and secondary hydrolysis steps, namely, ATP ADP + P. and ADP " AMP + P. 0The pH 4 hydrolyses were allowed to proceed for 24 hr, also at 70, to 40% completion. 

One of the major problems associated with the neutral hydrolysis method is that most of the impurities initially present in the PET waste remain in the TPA produced by the reaction. Therefore, complex and intensive purification operations are needed to obtain TPA with properties similar to the commercial grades. A hydrogenation step has been proposed as a method for the removal of impurities and colour found in the TPA produced by PET neutral hydrolysis.60 TPA precipitated from the hydrolysis medium is slurried in water and cata-lytically hydrogenated at 260-290 °C and a pressure of 65-82 atm for around 1 h. Palladium supported on carbon is one of the preferred catalysts for this hydrogenation step. This treatment leads to a colour level and fluorescence properties in the produced TPA similar to those of the commercially available virgin PET. 

Nucleophilic Opening. A neutral hydrolysis medium, more effective than water alone is provided by the combination of water and a polar aprotic solvent eg. HMPA or NMP (N-methyl-2-pyrrolidone). Thus 15 aqueous NMP at 130°C containing NaHCO will open terminal (but not internal) epoxides to diols (>90 ) as well as convert haloalkanes to alcohols in high yields. 

The reaction between carbanion and a formamide, R2NCHO [R = Me or R2 = 0(CH2CH2)2] yields a complex (Scheme 60, which again, depending on the hydrolysis medium, may be hydrolysed to jS-phosphorylated acetaldehyde (611) or to the enamine 612, and as before, 612 may be acidolysed to Azeotropic removal of water... 

Small samples of these hybrid resins can be prepared by simply mixing the alkoxysilane and aqueous silica sol using the water present in the sols as the hydrolysis medium. We have found that maintaining the pH on the acid side results in an adequate hydrolysis rate (lA) without an accompanying acceleration of silanol condensation (IB) that could result in the formation of highly crosslinked resin and gel particles. 

Tetryl, like RDX, is a solid at the temperatures in the hydrolysis reactor. For the neat tetryl in burster charges, the grain size depends on the extent to which the pressed explosive charges have been processed prior to being added to the hydrolysis reactor. The case of tetryl in tetrytol is quite different. TNT and tetryl are very similar chemically, so the solubility of tetryl in molten TNT is quite high (82 g/100 g TNT at 80°C [176°F] 149 g/100 g TNT at 100°C [212°F]) (Kaye and Herman, 1980). Tetryl in tetrytol is mostly dissolved in the TNT phase, so the rate of dissolution and subsequent reaction in the hydrolysis medium depends mainly on the TNT/tetryl droplet size and not on the particle size of the tetryl that was originally used to make the tetrytol. 

The reaction mechanism involves hydrolysis and polycondensation resulting in the hydrolyzed molecules with oxygen bridges. This leads to the formation of a skeleton, and hence, increases the viscosity of the sol inducing gelation. After completion of the hydrolysis reaetion, the obtained product had been collected, purified by Soxhlet extraction in cyclohexene and finally dried in a vacuum. Improvement of this process implies control of the particle morphology. The particles smaller than 10 nm with low polydispersity can be obtained [193-197] using the oil-water microemulsions as a hydrolysis medium of complex metal alkoxides. 

Four types of adsorbents are usually shared by SPE applications to herbicides. Hydrophobic modified silica materials (CIS, C8, C2, Cl) are extensively used for a large variety of samples (biological samples such as serum and urine for atrazine, simazine, prometryne, ametryn, sulfonyl ureas, or environmental samples such as different types of waters for alachlor, aldicarb, methiocarb - with concomitant hydrolysis -, medium polar, neutral, and alkaline herbicides, phenyl ureas). 

The next important parameter influencing the reaction rate is the pH of the silane hydrolysis medium. At high and very low pH values, the rate of hydrolysis is higher than that at neutral pH, at which silanes are most stable. For example, the rate of reaction of a monomeric trialkoxysilane in acetic add solution increases by a factor of... 

Another method for the hydroxylation of the etliylenic linkage consists in treatment of the alkene with osmium tetroxide in an inert solvent (ether or dioxan) at room temperature for several days an osmic ester is formed which either precipitates from the reaction mixture or may be isolated by evaporation of the solvent. Hydrolysis of the osmic ester in a reducing medium (in the presence of alkaline formaldehyde or of aqueous-alcoholic sodium sulphite) gives the 1 2-glycol and osmium. The glycol has the cis structure it is probably derived from the cyclic osmic ester ... 

Use of an excess of the halogenating agent results in halogenation at the 3-position of the oxindole[3,4]. The halogenation and hydrolysis can be carried out as two separate steps. One optimized procedure of this type used NCS as the halogenating agent and it was found that 70% phosphoric acid in 2-mcthoxycthanol was the most effective medium for hydrolysis[2]. If the halogenation is carried out in pyridine, the intermediate is trapped as an... 

Unlike the addition of concentrated sulfuric acid to form alkyl hydrogen sulfates this reaction is carried out m a dilute acid medium A 50% water/sulfuric acid solution is often used yielding the alcohol directly without the necessity of a separate hydrolysis step Markovmkov s rule is followed... 

A major advance was devised by Pehr Edman (University of Lund Sweden) that has become the standard method for N terminal residue analysis The Edman degrada tion IS based on the chemistry shown m Figure 27 12 A peptide reacts with phenyl iso thiocyanate to give a phenylthwcarbamoyl (PTC) denvative as shown m the first step This PTC derivative is then treated with an acid m an anhydrous medium (Edman used mtromethane saturated with hydrogen chloride) to cleave the amide bond between the N terminal ammo acid and the remainder of the peptide No other peptide bonds are cleaved m this step as amide bond hydrolysis requires water When the PTC derivative IS treated with acid m an anhydrous medium the sulfur atom of the C=S unit acts as... 

Under acidic conditions, furfuryl alcohol polymerizes to black polymers, which eventually become crosslinked and insoluble in the reaction medium. The reaction can be very violent and extreme care must be taken when furfuryl alcohol is mixed with any strong Lewis acid or Brn nstad acid. Copolymer resins are formed with phenoHc compounds, formaldehyde and/or other aldehydes. In dilute aqueous acid, the predominant reaction is a ring opening hydrolysis to form levulinic acid [123-76-2] (52). In acidic alcohoHc media, levulinic esters are formed. The mechanism for this unusual reaction in which the hydroxymethyl group of furfuryl alcohol is converted to the terminal methyl group of levulinic acid has recendy been elucidated (53). 

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