Solvent-free process

Higher alkoxides, such as tetra(2-ethylhexyl) titanate, TYZOR TOT [1070-10-6], can be prepared by alcohol interchange (transestenfication) in a solvent, such as benzene or cyclohexane, to form a volatile a2eotrope with the displaced alcohol, or by a solvent-free process involving vacuum removal of the more volatile displaced alcohol. The affinity of an alcohol for titanium decreases in the order primary > secondary > tertiary, and... 

It may even be possible to eliminate solids handling by processing in a solution. However, this may require an assessment of the hazards of a toxic or flammable solvent in a process compared to the hazards of the solvent-free process. 

Whilst total elimination of volatile organic solvents from all chemical manufacturing processes is a worthy goal, the pursuit of this goal must be subject to some caution. Alternative organic solvent-free processes may have poor heat and/or mass transfer and/or viscosity limitations, which could result in excessive energy use or the production of less pure... 

It is a misconception that most chemicals are manufactured in organic solvents. Most high-volume bulk chemicals are actually produced in solvent-free processes, or at least ones in which one of the reactants also acts as a solvent. Typical examples of such large-scale processes include the manufacture of benzene, methanol, MTBE, phenol and polypropylene. In addition, some heterogeneous gas-phase catalytic reactions, a class of solvent-free processes, are discussed in Chapter 4. 

In addition to solvent-free processing, phase-transfer catalytic conditions (PTC) have also been widely employed as a processing technique in MAOS [15]. In phase-transfer catalysis, the reactants are situated in two separate phases, for example liquid-... 

A survey of microwave activation in the chemistry of Hantzsch 1,4-dihydropyridines (1,4-DHP) has recently been reported [98]. The experimental method proposed more than a century ago remains the most widely used to synthesize these heterocycles. Since 1992 this process has been adapted to microwave irradiation under a variety of conditions to reduce the reaction time and enhance the yield. Among these experiments, Zhang [99] reported a solvent-free process starting from 3-aminocrotonate... 

Taking all criteria into consideration, aqueous two-phase techniques are very sound methods for homogeneously catalyzed processes such as hydrogenations or hydroformylations. Of the various alternatives to the conventional (and solvent-free) processes most progress in terms of ecological impact and economics has been attained by the aqueous biphasic approach (Figure 5.20). 

Solvent-free processing, 24 170-171 Solvent-free protocol, ecofriendly advantages of, 76 585 Solvent Green 3, 5, 28... 

As indicated in Table 3, reducing the excess methanol to only a 3 fold molar excess (rendering a nearly solvent free process) far exceeded expectations and allowed significant reductions in the catalyst levels. Under these conditions, catalyst turnover numbers exceeding 10,000 mol MPA/mol Pd were achieved with a turnover frequency of >3400 mol MPA/mol Pd/h. The reaction mixtures obtained from this process formed two liquid phases and the product spontaneously separated from the amine and amine hydrochloride. As a consequence of eliminating large methanol excesses, the methyl pivaloylacetate concentration in the product was raised to 26 wt. % without additional reaction time being required. This represents an additional ca. 2.5 fold improvement in reactor productivity. No attempt was made to reduce the methanol further. 

Solvent-free processes make use of neat or solid-state materials. Solvents or diluents that do not become incorporated into a final product are not used. 

Solvent-free processes can be energy-intensive. Applications can be limited by viscosity concerns and other physical constraints. Solvent-free syntheses sometimes yield lower-purity products than do traditional syntheses. 

The cyclization procedure of imines 56 was developed by using microwave heating in such high boiling solvents as yV-methylpyrrolidin-2-one at 150 °C, or even an ecofriendly solvent-free process in the presence of graphite at the same temperature <2003SC3795>. Yields are moderate (45-52%). 

Du Y, Cai F, Kong D-L et al (2005) Organic solvent-free process for the synthesis of propylene carbonate from supercritical carbon dioxide and propylene oxide catalyzed by insoluble ion exchange resins. Green Chem 7(7) 518-523... 

In another solvent-free process with the same lipase as above, trimethylene carbonate underwent an almost quantitative ring-opening polymerization in 120 h at 70 °C to form poly(trimethylene carbonate) [18]. No decarboxylation was detected (Scheme 4). w-Pentadecalactone was likewise polymerized with lipases in the absence of a solvent to form polyesters of high molecular weight [19]. 

J3 Reactive Extrusion for Solvent-Free Processing Facts and Fantasies... 

Certain quaternary salts of imidazoles have become important as ionic liquids, in particular salts of l-butyl-3-methylimidazolium (bmim). Preparation of imidazolium-containing ionic liquids, in the desired product ionic liquid as a solvent, is a virtually solvent-free, one-pot process proceeding in good to excellent yields <2003S2626>. There are also microwave-assisted, solvent-free processes for the preparation of imidazolium-based ionic liquids <2001CC643, 2003GC181>. 

Some new methods for the synthesis of the oxadiazole ring have been recently published. 1,2,4-Oxadiazoles can be easily obtained in a one-pot solvent-free process starting from P-keto esters 169 and amidoximes 170. The process is likely to go through an acyl ketene intermediate <07TL2231>. 

A new series of some spiro-1,4-dihydropyridines 2 has been synthesized by Hatamjafari [42] in good yields using a four-component, solvent-free process by the condensation of isatin, a primary amine, ethyl cyanoacetate and cyclohexanone absorbed on different solid supports under microwave irradiation applying a domestic oven. The report reveals that the application of montmorillonite KIO led to higher yields as compared to other solid supports (Scheme 2). 

Simple aromatic compounds such as benzene, alkylbenzenes, and halobenzenes (e. g., 12) arc nitrated in quantitative yield and with high para selectivity in a solvent-free process by the use of a mixture of nitric acid and acetic anhydride at 0-20 C in the presence of zeolite beta... 

Table 10.6 Summary of key advantages of Difasol (ionic liquid) process over the Dimersol (solvent free) process for alkene dimerization. ...

Akkar A, Namsolleck P, Blaut M, Muller RH. Solubilizing poorly soluble antimycotic agents by emulsification via a solvent-free process. AAPS Pharm Sci Tech 2004 5 E24. 

Supercritical fluid impregnation is often referred to as a solvent-free process because there is essentially no residual solvent to affect the properties of the processed materials. This approach demonstrates great potential for the preparation of new polymeric materials. Pioneering works by Sand (22) and Berens et al. (23) played an important role in stimulating interest in this area. Poliakoff (4) and Howdle (24) and their colleagues successfully used... 

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