Solvent-less

This procedure has been tested for a lot of bees and conditions are similar. Displl solvent and distill ketone with a water pump. My yield, 41 grams, about 75 %. Scaling. Of course. This procedure have been done with 150 cc of safrol, but with T75 I of methanol with simiair yields, so I ve prefered to present this version wich is better (less solvent, less time) Addition of nitrite i/vas done in 2,5 hours. When scaling, water in B can be decreased if we have problems with our volume flasks, but this means a lot of NaN02 is not dissolved, so each 15 minutes, we close sep. funnel, and shake B a bit, and when there is no foam, we can open sep. funnel again (1 drop or abit more /second). My opinion is 150 is ok, but theorically you can scale more. More time rxn is not a problem for product. 

Undoubtedly cost factors and environmental considerations (recycling of solvents, less toxic or less ha2ardous materials) wih lead to increasing industrial appHcation of this methodology. 

Since polar solvents would be expected to stabilize polar forms, a retreat towards the hydroxy tautomer (71) would be predicted in solvents less polar than water, and in the vapour phase. This is borne out in practice at equilibrium both 2- and 4-hydroxypyridine (as well as the 3-hydroxy compound, which even in water exists as an approximate 1 1 mixture of OH and NH forms) exist as such, rather than as the pyridinones. However, the 2- and 4-quinolinones remain in the NH (keto) forms, even in the vapour phase. Hydrocarbon or other solvents of very low polarity would be expected to give results similar to those in the vapour phase, but intermolecular association by hydrogen bonding often leads to a considerably greater proportion of polar tautomers being present than would otherwise have been predicted (77ACR186, 78JOC177). 

A solventless synthesis of pyrazoles, a green chemistry approach, has been described where an equimolar amount of the diketone and the hydrazine are mixed in a mortar with a drop of sulfuric acid and ground up. After an appropriate length of time ( 1 h) the product is purified to provide clean products. Even acyl pyrazoles 42 were obtained under the solvent-less reaction conditions in good yields. 

If the desired product is fairly water soluble, simple extraction into organic solvents may not be an efficient means of recovery. In that case, continuous extraction of the aqueous solution with an organic solvent may be necessary to effect the recovery. Either of two types of apparatus are normally employed, and the correct design depends on the density of the organic solvent. For solvents less dense than water, the apparatus should be set up as in Fig. A3.11a. The barrel of the extractor is charged with the... 

Fio. A3.11. Continuous extraction setups (a) for solvents less dense than water (b) for solvents more dense than water (c) Soxhiet extractor. 

Because of these observations, comparative experiments with peptides of different proline content in a solvent less polar than water, are recommended. (Pro-Pro-Gly)n and (Pro-Ala-Gly)n, in methanol/acetic add (volume ratio 9 1) show a temperature-induced triple helix-coil transition which is characterized by the following parameters92,150) (Pro-Pro-Gly)n AH°s = -1.9 kJ/rnol tripeptide AS° = -5.4 J tnor1 K (Pro-Ala-Gly) A HI = -0.9 kJ/mol tripeptide A 5° = -3.8 J mol-1 K ... 

Scheme 17 Solvent-less mercury(II)-assisted synthesis of oxazoles...

The addition of solutes decreases the freezing point of a solution. In the solution, solvent molecules collide with crystals of solid solvent less frequently than they do in the pure solvent. Consequently, fewer molecules are captured by the solid phase than escape from the solid to the liquid. Cooling the solution restores dynamic equilibrium because it simultaneously reduces the number of molecules that have sufficient energy to break away from the surface of the solid and increases the number of molecules in the liquid with small enough kinetic energy to be captured by the solid. 

Organic solvent-less techniques (e.g. subcritical water extraction, headspace SPME). 

SPE is an alternative rapid sample preparation mode for GC and HPLC (cf. Sections 7.1.1.2 and 7.1.1.6). Combination of SPE and SFE provides a solvent-less preparation technique. In this approach, the sample can... 

Many solvents may be used for this reaction the reaction rate, however, is greater in nonpolar solvents. Less color develops in the reaction mixture if the system is flushed with nitrogen at this point. 

This limiting velocity ( obsd caic) = (3 1) X 10 s is only 0.06% of the value of fesoiv = 0.049 s. This provides evidence that the ion pair reaction intermediate is trapped by solvent less than once for every 1000 times the... 

Both solid-solid and solid-gas types of reactions lead from solid reactants to a solid product without the use of solvents. Solvent-less processes, however, are not necessarily solid-state processes. Indeed, it has been argued [8d,e] that many solid-state syntheses cannot be regarded as bona fide solid-solid reactions because they occur with the intermediary of a liquid phase, such as a eutectic phase or a melt, or may require destruction of the crystals prior to reaction. This latter situation is often observed, for instance, in the case of reactions activated by co-grinding, since the heat generated in the course of the mechanochemical process can induce local melting at the interface between the different crystals, or when kneading, i.e. grinding in the presence of small amounts of solvent, takes place (vide infra). 

Pellizzari reported in 1884 a study of the reaction of dry ammonia vapours with dried and pulverized phenols and carboxyhc acids [17]. However, in spite of this early beginning, a systematic exploration of solvent-less processes of this type was not undertaken until the early 1970s by Paul and Curtin [18-20] and subsequently by others [21]. 

In this chapter we have described two classes of solvent-less chemical reactions those occurring between molecular solids (mter-solid reactions) to yield a new crystalline solid, and those occurring between a molecular solid and a gas (solid-gas reactions) to yield a solid product. We have also described solid-state reactions taking place between molecules within a crystal (intra-solid reactions). The distinction between intra- and inter-solid reactions carries no implications for the reaction mechanisms, which we have decided not to discuss. Indeed, the mechanical stress produced by grinding or milling together two solids, as in the case of inter-solid reactions, may well generate molecular... 

The imidates (62) also serve as nitrile yhde synthons via cycloaddition and subsequent spontaneous elimination of ethanol (34,35). Cycloadditions were carried out to aldehydes, leading to 2-oxazolines (e.g., 64) and to isocyanates and isothiocyanates. In the preparation of the 2-oxazolines, a solvent-less mixture of the imidate and the required aldehyde were heated at 70 °C and the cycloadducts 64 (R=Ph, 2-furyl, Mc2CH, 2-HO C6H4, 2-pyridyl, cinnamyl) were isolated in yields of 64—91%. 

The utility of carbodiimide reagents was too important to consider abandoning them. Instead, it rapidly became obvious that carbodiimide activation could be used to prepare in situ active esters. Numerous nucleophilic additives were discovered and prepared for use in these reactions. The most important of these additives was 1,2,3-benzotriazol-l-ol (HOBt, 1), first reported for use in peptide synthesis by Konig and Geiger in 1970.[2(l As an example of a typical result, 1.2 equivalents of HOBt was added to the DCC coupling of Boc-Leu-Phe-OH to H-Val-OtBu in DMF as a solvent. Less than 1% of the l-d-l epimerized tripeptide was formed. When the reaction was carried out in the absence of HOBt, the amount of l-d-l product formed was 14.3%. Addition of HOBt to DCC reactions converts the intermediate G-acylisourea (2) (and any symmetrical anhydride) into the HOBt active ester 3 (Scheme 8). 

A growing cadre of scientists is finding ways to reduce pollution, not by changing existing products, but by inventing cleaner ways to make them. Discusses some work in solvent-less chemistry. (Chase, 1995)... 

Toluene (methylbenzene) does not possess the myelotoxic properties of benzene, nor has it been associated with leukemia. It is, however, a central nervous system depressant and a skin and eye irritant. It is also fetotoxic. See Table 56-1 for the TLVs. Exposure to 800 ppm can lead to severe fatigue and ataxia 10,000 ppm can produce rapid loss of consciousness. Chronic effects of long-term toluene exposure are unclear because human studies indicating behavioral effects usually concern exposures to several solvents. In limited occupational studies, however, metabolic interactions and modification of toluene s effects have not been observed in workers also exposed to other solvents. Less refined grades of toluene contain benzene. 

A. 1,2,4-Thiadiazole and Homoloqs The parent compound, first obtained in 1955, is a volatile liquid, soluble in polar solvents, less so in non-polar ones. Its physical properties are summarized in Table II. Its I.R. spectrum has been recorded.8... 

When more satisfactory forms of diffusion coefficient for the hydro-dynamic repulsion effect become available, these should be incorporated into the diffusion equation analysis. The effect of competitive reaction processes on the overall rate of reaction only becomes important when the concentration of both reactants is so large that it would require exceptional means to generate such concentrations of reactants and a solvent of extremely low diffusion coefficient to observe such effects. This effect has been the subject of much rather repetitive effort recently (see Chap. 9, Sect. 5.5). By contrast, the recent numerical studies of reactions between uncharged species is a most welcome study of the effect of this competition in various small clusters of reactants (see Chap. 7, Sect. 4.4). It is to be hoped that this work can be extended to reactions between ions in order to model spur decay processes in solvents less polar than water. One other area where research on the diffusion equation analysis of reaction rates would be very welcome is in the application of the variational principle (see Chap. 10). 

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