Clathrates acetic acid

Fig. 32. Packing relations and steric fit of the 26 acetic acid (1 1) clathrate (isomorphous with the corresponding propionic acid clathrate of 26)1U- (a) Stereoscopic packing illustration acetic acid (shown in stick style) forms dimers in the tunnel running along the c crystal axis of the 26 host matrix (space filling representation, O atoms shaded), (b) Electron density contours in the plane of the acetic acid dimer sa First contour (solid line) is at 0.4 eA" while subsequent ones are with arbitrary spacings of either 0.5 and 1 eA 3. Density of the enclosing walls comes from C and H atoms of host molecules.

A further example of the steric fit and thus the conditions of the second rank interactions between host and guest is illustrated by the channel structure of the acid inclusions of 26 (see inclusion compound with acetic acid, Fig. 32a). The tunnel has a mostly hydrophobic character being made up mainly from the aromatic portions of the roof-shaped host molecule. We must note that this arrangement applies possibly for the acetic acid clathrate of 1 as well. 

Clathrate formation is very attractive for exploitation in solid-state chemistry. It allows one to modify in a simple way the environment of the guest molecule, to place this molecule in a crystalline phase with a structure different from its own (one structure may be chiral, and the other not), and even to achieve a stable crystalline structure at a temperature above the melting point of the pure guest. Some of the variety available for a single compound, acetic acid, is... 

Reduction of a,/3-unsaturated to saturated ketones was further achieved by electrolysis in a neutral medium using copper or lead cathodes (yields 55-75%) [766], with lithium in propylamine (yields 40-65%) [876], with potassium-graphite clathrate CgK (yields 57-85%) [807], and with zinc in acetic acid (yield 87%) [688]. Reduction with amalgamated zinc in hydrochloric acid (Clemmensen reduction) usually reduces both functions [877]. 

Fig. 32. Packing relations and steric fit of the 26 acetic acid (1 1) clathrate (isomorphous with the corresponding propionic acid clathrate of (a) Stereoscopic packing illustration acetic acid...

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