Synthesis from Solutions

In these techniques the crystals precipitate from a saturated or supersaturated solution. 

Sol-gel growth techniques. The most common example is the production of synthetic opal. The first step consists to produce a suspension of monodisperse silica nanospheres in ethanol obtained by the direct hydrolysis of tetraethyl ester of orthosilicic acid, SifOC H l with ethanol using ammonia as a catalyst according to the following reaction  

SiCOCjHj), + 4H,0 — Si(OH), + 4C,H30H Simultaneously, the polymerization of orthosilicic acid occurs by the reaction  

By adding further amounts of reactant, the particles of silica grow up to the diameter de-sired-that is to about 300 nm size. Secondly, the raw opal precursor is precipitated either by spontaneous sedimentation or by centrifugation. Finally, the opal precursor is then dried in order to remove liquid from its pores. Afterwards, the dried opal precursor is sintered by thermal treatment at 400-800°C in a furnace. For the production of synthetic opal of gem quality, it is then necessary to complete the process by filling pores in the opal substance with a silica gel. 

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Jolivet J-P (2000) Metal Oxide Chemistry and Synthesis. From Solution to Solid State. Wiley, Chichester... 

Jolivet J-P. Metal Oxide Chemistry and synthesis - From solution to solid state John Wiley Sons Ltd Chichester, 2000. 

Jolivet, J.P., Livage, J. and Henry, M. (2000). Metal Oxide Chemistry and Synthesis From Solution to Oxide. John Wiley Sons, Ltd, Paris. 

Jolivet JP. Metal oxide chemistry and synthesis from solution to sohd state. Chichester Wiley 2000. 

Corbel G., Courbion G., Le Berre F., Leblanc M., Le Meins JM., Maisonneuve V., Mercier N. Synthesis from solutions and properties of various metal fluorides and fluoride salts. J. Fluorine Chem. 2001 107 193-198... 

M.p. 190-192 C. The enolic form of 3-oxo-L-gulofuranolactone. It can be prepared by synthesis from glucose, or extracted from plant sources such as rose hips, blackcurrants or citrus fruits. Easily oxidized. It is essential for the formation of collagen and intercellular material, bone and teeth, and for the healing of wounds. It is used in the treatment of scurvy. Man is one of the few mammals unable to manufacture ascorbic acid in his liver. Used as a photographic developing agent in alkaline solution. 

Two molecules of vitamin A are formed from one molecule of -carotene. Vitamin A crystallizes in pale yellow needles m.p. 64 C. It is optically inactive. It is unstable in solution when heated in air, but comparatively stable without aeration. Vitamin A is manufactured by extraction from fish-liver oils and by synthesis from / -ionone. The role of vitamin A in vision seems to be different from its systemic function. See also relincne and rhodopsin. 

Pyrimidines have also served as electrophiles in crown synthesis from this group. 4,6-Dichloropyrimidine reacts with diethylene glycol and sodium hydride in anhydrous xylene solution to form the 20-crown-6 derivative as well as the other products shown in Eq. (3.48). Note that a closely related displacement on sy/rr-trichlorotriazine has been reported by Montanari in the formation of polypode molecules (see Eq. 7.5). 

The structure of this compound is confirmed by the preparation of the 1-acetyl derivative, acid degradation to 4-methylquinoxalin-3-one-2-carboxylic acid (12), and alternative synthesis from the acid chloride of (12) and AW -dimethyluread A most unusual cyclization occurs when AW-dimethyl-o-phenylenediamine (15) is treated with alloxan in ethanolic solution this apparently involves an A-methyl group and leads to the formation of the spirobarbituric acid (16). The struc-... 

The palladium compound [Pd(CNcy)2]3 has been made by metal vapour synthesis, from Pd atoms and a solution of cyNC at 160 K. It has an analogous structure [Pd3(CNcy)3( 2-CNcy)3] [60]. 

PA-4,6 synthesis from, 171-172 PA-6,6 polymerization from, 169-170 PA-6,1 synthesis from, 181 PA salt solution, polymerization from, 164 Pawlow, James H., 431 PBIs. See Polybenzimidazoles (PBIs)... 

Empirical kinetics are useful if they allow us to develop chemical models of interfacial reactions from which we can design experimental conditions of synthesis to obtain thick films of conducting polymers having properties tailored for specific applications. Even when those properties are electrochemical, the coated electrode has to be extracted from the solution of synthesis, rinsed, and then immersed in a new solution in which the electrochemical properties are studied. So only the polymer attached to the electrode after it is rinsed is useful for applications. Only this polymer has to be considered as the final product of the electrochemical reaction of synthesis from the point of view of polymeric applications. 

Metal clusters on supports are typically synthesized from organometallic precursors and often from metal carbonyls, as follows (1) The precursor metal cluster may be deposited onto a support surface from solution or (2) a mononuclear metal complex may react with the support to form an adsorbed metal complex that is treated to convert it into an adsorbed metal carbonyl cluster or (3) a mononuclear metal complex precursor may react with the support in a single reaction to form a metal carbonyl cluster bonded to the support. In a subsequent synthesis step, metal carbonyl clusters on a support may be treated to remove the carbonyl ligands, because these occupy bonding positions that limit the catalytic activity. 

Supported metal carbonyl clusters are alternatively formed from mononuclear metal complexes by surface-mediated synthesis [5,13] examples are [HIr4(CO)ii] formed from Ir(CO)2(acac) on MgO and Rh CCOlie formed from Rh(CO)2(acac) on y-Al203 [5,12,13]. These syntheses are carried out in the presence of gas-phase CO and in the absence of solvents. Synthesis of metal carbonyl clusters on oxide supports apparently often involves hydroxyl groups or water on the support surface analogous chemistry occurs in solution [ 14]. A synthesis from a mononuclear metal complex precursor is usually characterized by a yield less than that attained as a result of simple adsorption of a preformed metal cluster, and consequently the latter precursors are preferred when the goal is a high yield of the cluster on the support an exception is made when the clusters do not fit into the pores of the support (e.g., a zeolite), and a smaller precursor is needed. 

The field of surface-mediated synthesis of metal carbonyl clusters has developed briskly in recent years [4-6], although many organometallic chemists still seem to be unfamiliar with the methods or consider themselves ill-equipped to carry them out. In a typical synthesis, a metal salt or an organometallic precursor is brought from solution or the gas phase onto a high-area porous metal oxide, and then gas-phase reactants are brought in contact with the sample to cause conversion of the surface species into the desired products. In these syntheses, characteristics such as the acid-base properties of the support influence fhe chemisfry, much as a solvenf or coreactant influences fhe chemisfry in a convenfional synfhesis. An advanfage of... 

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