Syntheses in Aqueous Solution

The first demonstration of in vitro P3HB synthesis in aqueous solution was achieved by Gerngross and Martin [35]. The polymer obtained had significantly higher molecular weight than that synthesized in vivo. This is probably due to a lack of a chain termination step of the PHA polymerization under in vitro conditions, similar to a living polymerization. Many other reports followed [27, 36, 38-44] and were extensively reviewed [2, 6, 7, 12, 26-32]. 

These investigations have demonstrated the successful application of cyclodex-trins in polymer synthesis in aqueous solutions via free radical polymerization or via a oxidative recombination mechanism. Some special aspects of cyclodextrins were found concerning the kinetics, chain transfer reaction, and copolymerization parameters [63],... 

The stepwise addition of N-carboxy a-amino acid anhydrides to amino acids or peptides in organic solvents is well documented (for review see Refs. 69 and 70). More recently the method has been applied to peptide synthesis in aqueous solutions (71,72,73). Novel syntheses of N-substituted carboxyanhydrides of a-amino acids have been carried out (74,75) and the crystal molecular structures of several of them have been determined (76,77,78). 

M.W. Hosseini, J.M. Lehn, Supramolecular Catalysis of Adenosine-Triphosphate Synthesis in Aqueous-Solution Mediated by a Macrocyclic Polyamine and Divalent Metal-Cations , J. Chem. Soc., Chem. Commun., 451 (1991)... 

As potential materials for preventing common metals from corrosion, PPy and its derivatives have attracted much attention due to their advantageous properties such as ease of synthesis in aqueous solution and high stability in the oxidized state. In general, PPy films on inert anodes such as platinum, glassy carbon, stainless steel, and gold can be easily polymerized electrochemically in aqneous or organic media. However, in the case of electrochemical polymerization on the oxidizable metals, dissolution of metal occurs before electrochemical polymerization does, because the oxidation potentials of these... 

See for example Moschetto, G., R. Lauceri, F.G. Gulino, D. Sciotto, and R. Purreho (2002). Non-covalent synthesis in aqueous solution of discrete multi-porphyrin aggregates with programmable stoichiometry and sequence. J. Am. Chem. Soc. 124(49), 14536-14537 and references cited therein. 

MacLaren, I., Ponton, C.B. A TEM and HREM study of particle formation during barium titanate synthesis in aqueous solution. J. Eun Ceram. Soc. 20, 1267-1275 (2000)... 

OF and Lipase P were also shown to aggregate with block copolymers made of poly[(A-acetylimino)ethylene] and poly[(A-pentanoylimino)ethylene], with about 30% increased activity for the ester hydrolysis and 200% increased activity for the ester synthesis in aqueous solutions compared to the native enzymes. The activity of egg white lysozyme located in the core of PEG—poly(o ,j8-aspartic acid) micelles was investigated by colorimetric methods and revealed an increase for p-nitrophenyl-penta-A-acetyl-/ -chitopentaoside as substrate. By the determination of kinetic constants of enzymatic reaction, it was demonstrated that the increase in the enzymatic activity was... 

Finally, gibbsite can be envisaged as a template for developing new nanostructured materials such as imogolite-like NTs. The mild conditions for the synthesis in aqueous solutions make them very attractive for technological and environmental applications. 

There exist a number of d -synthons, which are stabilized by the delocalization of the electron pair into orbitals of hetero atoms, although the nucleophilic centre remains at the carbon atom. From nitroalkanes anions may be formed in aqueous solutions (e.g. CHjNOj pK, = 10.2). Nitromethane and -ethane anions are particularly useful in synthesis. The cyanide anion is also a classical d -synthon (HCN pK = 9.1). 

Another difficulty in this reaction lies in the preparation of pure chloroacetaldehyde. The low yield observed is due to simultaneous formation of by-products (polyhalogenation). So vinylchloride was used as a starting material for this synthesis (449). A simpler method is to react chlorine with vinylchloride in aqueous solution and then to dehydrate the semihydrated chloroacetaldehyde by distillation through a column of calcium chloride heated to 70 to 90 C (451). 

The first reported synthesis of acrylonitrile [107-13-1] (qv) and polyacrylonitrile [25014-41-9] (PAN) was in 1894. The polymer received Htde attention for a number of years, until shortly before World War II, because there were no known solvents and the polymer decomposes before reaching its melting point. The first breakthrough in developing solvents for PAN occurred at I. G. Farbenindustrie where fibers made from the polymer were dissolved in aqueous solutions of quaternary ammonium compounds, such as ben2ylpyridinium chloride, or of metal salts, such as lithium bromide, sodium thiocyanate, and aluminum perchlorate. Early interest in acrylonitrile polymers (qv), however, was based primarily on its use in synthetic mbber (see Elastomers, synthetic). 

A Methylamino)phenol. This derivative, also named 4-hydroxy-/V-methy1ani1ine (19), forms needles from benzene which are slightly soluble in ethanol andinsoluble in diethyl ether. Industrial synthesis involves decarboxylation of A/-(4-hydroxyphenyl)glycine [122-87-2] at elevated temperature in such solvents as chlorobenzene—cyclohexanone (184,185). It also can be prepared by the methylation of 4-aminophenol, or from methylamiae [74-89-5] by heating with 4-chlorophenol [106-48-9] and copper sulfate at 135°C in aqueous solution, or with hydroquinone [123-31 -9] 2l. 200—250°C in alcohoHc solution (186). 

Acid—Base Catalysis. Inexpensive mineral acids, eg, H2SO4, and bases, eg, KOH, in aqueous solution are widely appHed as catalysts in industrial organic synthesis. Catalytic reactions include esterifications, hydrations, dehydrations, and condensations. Much of the technology is old and well estabhshed, and the chemistry is well understood. Reactions that are cataly2ed by acids are also typically cataly2ed by bases. In some instances, the kinetics of the reaction has a form such as the following (9) ... 

The following synthesis of p ewdopelletierine is of special interest, since it involves only materials and conditions which could occur in plants and is therefore a possible bio-synthesis. Menzies and Robinson showed that when calcium acetonedicarboxylate, glutardialdehyde and methyl-amine are mixed in aqueous solution under specified conditions and the mixture is kept for twenty-four hours, a produet (XX) is formed, which can be decarboxylated to -pelletierine (XXI) and the latter isolated as the picrate, whieh after recrystallisation yields the pure base (m.p. 48-5°), the identity of which can be established by eonversion to the characteristic dipiperonylidene derivative. The course of the synthesis is represented as follows — ... 

The reaction is used for the chain extension of aldoses in the synthesis of new or unusual sugars. In this case, the starting material, L-arabinose, is an abundant natural product and possesses the conect configurations at its three chirality centers for elaboration to the relatively rare L-enantiomers of glucose and mannose. After cyanohydrin formation, the cyano groups are converted to aldehyde functions by hydrogenation in aqueous solution. Under these conditions, —C=N is reduced to —CH=NH and hydrolyzes rapidly to —CH=0. Use of a poisoned palladiurn-on-barium sulfate catalyst prevents further-reduction to the alditols. 

Hydroxylamine can be prepared by a variety of reactions involving the reduction of nitrites, nitric acid or NO, or by the acid hydrolysis of nitroalkanes. In the conventional Raschig synthesis, an aqueous solution of NH4NO2 is reduced with HS04 /S02 at 0° to give the hydroxylamido-A ,A -disulfate anion which is then hydrolysed stepwise to hydroxylammonium sulfate ... 

The decarboxylated products are obtained directly, however, if condensation of tryptamine with the a-oxo acid is carried out in aqueous solution at elevated temperature. This direct synthesis of a l-substituted-l,2,3,4-tetrahydro-j8-carboline has been carried out with... 

Alpert has shown [47] that poly(succinimide)-silica can be further hydrolyzed to poly (aspartic acid)-silica or condensed with [3-alanine in aqueous solution to form a covalently bonded copolymer of 2-carboxyethyl aspartamide and aspartic acid. The content of carboxyl groups generated by this way has not been quantified directly, but the cation-exchange hemoglobin capacity has been measured for a series of the packings. Thus, the optimal concentration of poly(succinimide) used in the synthesis was found to be 2 5%. 

Oxidation of phenyl hexyl sulphide with sodium metaperiodate gave also only a trace amount of the corresponding sulphoxide72. On the other hand, Hall and coworkers73 prepared benzylpenicillin and phenoxymethyl penicillin sulphoxides from the corresponding benzyl esters by oxidation with sodium metaperiodate in dioxane solution with a phosphate buffer. A general procedure for the synthesis of penicillin sulphoxides was reported later by Essery and coworkers74 which consists in the direct oxidation of penicillins or their salts with sodium metaperiodate in aqueous solution at pH 6.5-7.0. 1-Butadienyl phenyl sulphoxide 4475 and a-phosphoryl sulphoxides 4576 were also prepared by the same procedure. 

A. and Angel O. Z. (2008). Synthesis and spectral properties of starch capped CdS nanoparticles in aqueous solution J. Cryst. Growth, 310,160-164. 

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