Alcohols for Finishing

by Jeff Jewitt

Alcohol's are important solvents in finishing. If you see a chemical compound with the "ol" as a suffix its an alcohol. You can have a low molecular weight alcohol like methanol (CH3OH) or a high molecular weight alcohol like glycerol (CH2OH.CHOH.CH2OH). What they all have in common is what chemists call a functional group - in this case it's the OH group - called a hydroxyl group. The number of hydroxyl groups determine whether it's an alcohol or a polyol (containing more than one hydroxyl groups) The most common ones are what chemists call the lower alcohols. In order of increasing molecular weight they are:

• Methanol - prepared by a reaction between carbon dioxide and Hydrogen. It is poisonous and because of the small size of the molecule - it will pass through an organic vapor respirator. Synonyms are methyl alcohol and wood alcohol (because it used to be prepared from the burning of wood and distillation of the vapor.) In Canada and Britain is called methyl hydrate.
• Ethanol - this is what is meant when the word "alcohol" is used. Ethanol is produced from corn and is booze - and as such all ethanol production and use is regulated by the BATF. There are 4 types - pure ethanol, SDA (specially denatured alcohol), "industrial" alcohol and CDA (completely denatured alcohol..)
• Pure, (undenatured) alcohol may be purchased by consumers as liquor or Grain alcohol in which a hefty tax is applied. It may also be purchased on a tax-free or tax-paid basis. Approved educational scientific medical and public agencies may buy pure ethanol provided it is not used in food or beverage products. Tax paid industrial alcohol is pure ethanol which has been released from federal bond only after payment of a substantial federal tax. A kickback is given if the resulting product made is a medicine, food or food flavoring product or any other product unfit for consumption. It is also used as a chemical intermediate for the processing of cosmetics. Note that the Government wants a tax only if ethanol is used for a beverage (i.e. liquor.)
• SDA - is the most important commercial from of ethanol. There are over 50 formulas for denaturing - depending on the end use. For example Formula 1 is 4 gallons methanol, 1 gallon of MIBK per 100 gallons of ethanol. Formula #40a is Butyl alcohol and Sucrose Octaacetate. You will find this in say mouthwash. If more than 4 % by weight of methanol is used a Poison sign with the skull and crossbones is required. The whole idea of denaturing is to make you very ill if you drink the stuff. Formula #1 can kill you. Formula #40a will probably make you very sick. SDA is used in cosmetics, toiletries and medicines. Its purchase it still tightly controlled and consumers never are able to buy SDA
• Industrial alcohol is the stuff that is used to make lacquers, inks and other products. It can be purchased with out a permit.
• CDA - is completely denatured alcohol and this is the stuff you buy in the can at the paint store. Its purchase and sale is not regulated as much. One of the big problems is that we as consumers never know what denatured alcohol formula we are getting when we buy alcohol at the paint store. Most of the time its methyl alcohol with other solvents added.
• Propanol --- this alcohol exhibits isomerism - a chemical term that means that it can exist in several different forms because the hydroxyl group (OH) can be bonded to different carbon atoms. Thus you have propanol or isopropanol. The "normal" position of the hydroxyl group usually is referred to with the n designation or n-propanol.
• Butanol - because of the 4 carbon atoms - you have more isomers. So you can have butanol or isobutanol.

The differences in toxicity and other physical properties between an alcohol and its isomer can be dramatic. Isopropanol is less toxic than propanol - which is why you find it in rubbing alcohol. The boiling point difference between n-butanol and isobutanol is 10 degrees.