Solvents drying

In organic solvent recovery the most common separation is the removal of water. Water has many harmful effects on a solvent. Firstly, it can spoil its solvent power and this may call for a reduction of water to, say, 1%. 

It can slow down a reaction as one finds in, for instance, esterification. Here a water content of 0.1% is likely to be about the economic optimum. 

It can destroy a urethane or even a costly high molecular weight Grignard reagent on a mole for mole basis and a water content of 100 ppm or even less may be demanded by process economics. Indeed, an economic case can sometimes be made to dry a virgin solvent immediately before use. 

At the same time solvents range from those miscible with water in all proportions to those in which water is very sparingly soluble though always detectable. Furthermore there are a number of solvents e.g. butyl cellosolve, MEK and THF that have lower as well as upper critical solution temperatures (LOST and UCST, respectively). 

With this range of process requirements and problems it is not surprising that there are many drying methods from which to choose  

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Barium perchlorate. Expensive. Used in desiccators (covered with a metal guard). Unsuitable for drying solvents or organic material where contact is necessary, because of the danger of EXPLOSION... 

Rapid purification Check for peroxides (see Chapter 1 and Chapter 2 for test under ethers). Pre-dry with CaCl2 or better over Na wire. Then reflux the pre-dried solvent over Na (1 % w/v) and benzophenone (0.2% w/v) under an inert atmosphere until the blue colour of the benzophenone ketyl radical anion persists. Distil, and store over 4A molecular sieves in the dark. 

SOLVENTS Liquids that dissolve other substances. Chemical solvents are used widely in industry e.g. by pharmaceutical makers to extract active substances by electronics manufacturers to wash circuit boards by paint makers to aid drying. Solvents can cause air and water pollution and some can be responsible for ozone depletion. 

Dry scrubber An absorption system which uses a dry solvent directly injected into the gas stream. 

In order to obtain good yields, it is important to use dry solvent and reagents. The commercially available t-butyl hydroperoxide contains about 30% water for stabilization. For the use in a Sharpless epoxidation reaction the water has to be removed first. The effect of water present in the reaction mixture has for example been investigated by Sharpless et al. for the epoxidation of (E)-a-phenylcinnamyl alcohol, the addition of one equivalent of water led to a decrease in enantioselectivity from 99% e.e. to 48% e.e. 

The column is eluted with dry solvents of gradually increasing eluting power. The order of eluting power of the common dry solvents is shown in Table A3.5. The compounds are eluted from the column in order of their increasing polarity. The usual order of elution of organic compounds is shown in Table A3.6, The progress of the... 

Type of binder Mode of drying Solvents Acid resistance Alkali resistance Water resistance Solvent resistance Exterior weathering resistance Special features... 

Vinyl resins Air drying Solvent evaporation Blends usually rich in ketones Very good Very good Very good Poor Good Fire hazard Flash point usually below 23°C... 

Chlorinated rubber Air drying Solvent evaporation Aromatic hydrocarbons Good Good Very good Poor Good Very poor heat resistance... 

Cellulose nitrate Air drying Solvent evaporation Blends of esters, alcohols and aromatic hydrocarbons Fairly good Bad Good Poor Very good Fire hazard Statutory regulations governing use... 

When the word alcohol is used alone, it refers to ethanol, the alcohol found in wine, beer, and distilled spirits. Ethanol is used as a fast-drying solvent in many products, especially cosmetics and hairsprays. 

Transition-metal-based Lewis acids such as molybdenum and tungsten nitro-syl complexes have been found to be active catalysts [49]. The ruthenium-based catalyst 50 (Figure 3.6) is very effective for cycloadditions with aldehyde- and ketone-bearing dienophiles but is ineffective for a,)S-unsaturated esters [50]. It can be handled without special precautions since it is stable in air, does not require dry solvents and does not cause polymerization of the substrates. Nitromethane was the most convenient organic solvent the reaction can also be carried out in water. 

At a Pt-[0s(bipy)2(4-vinylpyridine)2](C10J -Au sandwich electrode (see Sect. 5.2.1) plateau-like voltammograms are observed in the dry, solvent-free state when... 

If gaseous S2O-SO2 mixtures are dissolved in dry solvents such as CS2, CCI4, CHCI3, CH2CI2, and liquid SO2 at temperatures between -75 and -1-25 °C, intense yellow solutions of polysulfuroxides are obtained which have been characterized only very poorly [19]. In contrast to the opinion of some authors [20], S2O cannot be detected in such solutions, e.g., by infrared spectroscopy. Most probably, mixtures of cyclic polysulfuroxides are present besides SO2 (see below, in particular the preparation of S5O), e.g. ... 

If, however, you are still soldiering on with a spectrometer of 100 MHz or less, then by all means try using them to stretch a spectrum out - if your compound is suitable. They work by coordinating with an atom that has a lone pair of electrons available for donation. The more available the lone pair, the greater will be the affinity (-NH2/NHR > -OH > >C=0 > -O- > -COOR > -CN). Note that they will only work in dry solvents that don t contain available lone pairs. Good luck ... 

Rapid addition of bromine to the dried solvent to make a 10% solution caused a vigorous reaction with gas evolution. As this happened in a newly installed brightly illuminated fume cupboard lined with a reflective white finish, photocatalysed bromination of the solvent may have been involved, as has been observed in chlorine-ether systems. 

A mixture of the hydride and solvent was heated to, and held at 50°C. An exothermic reaction, which increased the temperature to 75°C, could not be controlled by external cooling, and the pilot-scale reactor contents erupted. It was later found that an exotherm began to develop at 26° (or at 40-50° with carefully dried solvent), and the subsequent reaction accelerated rapidly. Avoidance of holding mixtures hot is recommended, particularly when scaling up reactions. Similar behaviour was seen with dimethylacetamide [1], A further similar plant-scale incident was reported, with onset of the exotherm at 40°C, followed by self-heating to 100°C in 10 min, even with maximum cooling applied [2],... 

MS6C6(CF3)6] complexes are easily reduced to the univalent anion. Dry solvents and apparatus must be employed. Adequately dry solvents may be obtained by storage over molecular sieves. 

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