Sublimation menthol

Liquids with high vapor pressures at ordinary temperatures are said to be volatile. Methanol (vapor pressure 98 Torr at 20°C) is highly volatile mercury (1.4 mTorr) is not. Solids also exert a vapor pressure, but their vapor pressures are usually much lower than those of liquids because the molecules arc gripped more tightly in a solid than they are in a liquid. Nevertheless, solids vaporize in the process called sublimation (Section 6.11), which we can observe in the presence of some pungent solids—such as menthol and mothballs. 

Menthol 0.003-0.015% in suspensions, and syrups Cooling effect Sublimes easily above 25° C and composition of natural oil may vary with source Incompatible with thymol, phenol, camphor, and other excipients Slightly soluble in glycerin very soluble in alcohol... 

Mandelic acid sublimation, 280 Mandelonitrile, 233, 330 Melting point, enantiomers, 279 Menthol, 9... 

Menthol should be stored in a well-closed container at a temperature not exceeding 25°C, since it sublimes readily. 

Appearance colorless, prismatic or acicular, shiny crystals, without the characteristic odor, taste, and cooling effect of /-menthol. The crystalline form may change with time owing to sublimation within a closed vessel. 

Materials held together by van der Waals attractions often have a smell at room temperature (e.g., camphor and menthol). This is caused by the molecules escaping from the solid and subliming directly into the gas phase. The attractive forces between the molecules are weak. These forces arise from distortions in the electron cloud around the molecule, which cause some parts to be relatively positively charged, while other parts are relatively negative. 

White, odorless Crystals, mp 131-133. Becomes grayish on exposure to air and light. Poisonous d 1.45 bp 309. Sublimes when slowly heated. One gram dissolves in 1.7 ml water, 1.3 ml ale, 1.6 ml ether slightly sol in benzene, chloroform, carbon disulfide. The aq soln darkens on exposure to air, quite rapidly when alkaline. Keep well closed and protected from tight. Incompat. Alkalies, ammonium hydroxide. antipyrine. camphor, phenol, menthol. LDH orally in rabbits 1.6 g/kg (Dollahite). 

In another variation of the RESS process, referred to as RESS-SC, a solid cosolvent such as menthol was used to modulate the solubility of the drug (phenytoin) in the polymer (Thakur and Gupta 2006). It was shown that when drug particles were mixed with solid cosolvent such as menthol, the presence of solid cosolvent inhibited particle-particle interactions between drug particles, thereby hindering the crystal growth. As illustrated in Eig. 19.2, phenytoin particles are surrounded by menthol, which reduced interparticulate interactions with other phenytoin particles. The cosolvent (menthol) is then removed by downstream processing such as sublimation or lyophilization. 

Menthol, like camphor, is a waxy crystalline solid that sublimes at room temperature. It is, however, more polar and dissolves in alcohols. 

The solid, subliming materials - camphene, tricyclene, menthol and cyclododecane - have been used as temporary, volatile consolidants and release agents (lagers lagers, 1999 Cleere, 2005). These have been chosen to be suitable because of their ease of use and resistance to polar solvents. Of these, cyclododecane is the preferred material because it is the most stable to degradation, has fewer impurities, and has fewer health and safety risks. It is important that the material applied contains as little as possible non-volatile material, which will remain after treatment as a contaminant. 

These materials are applied to fragile surfaces either in solution or molten. Films applied from different solvents tend to deposit as crystals so are less coherent and resistant to penetration by liquids, such as water. Films applied from molten materials are stronger, more coherent and solvent resistant. Mixtures of compounds may form strong films with smaller crystals, by analogy with similar findings from industrial practice (Araki and Halloran, 2004). The rate of sublimation of the consolidant depends on the vapour pressure of the material, the temperature, the rate of air movement and the depth of penetration into a porous surface. For the high-melting-point, low-volatility materials such as cyclododecane and menthol, it can take many weeks for the consolidant to leave. The more volatile materials will leave faster. 

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