Science Makes Sense Week 15: Organic Chemistry, organic acids, alcohol, illicit liquor and alpha-hydroxy acids.


My supervisor in Chicago used to add a slice of lemon every time he drank water.   I tried doing that for a while but that habit was short-lived.  Now I hear again about the benefits of drinking warm water in the morning with lemon-juice. (Ref.1)  Apparently it aids digestion and helps in many other ways.  Cooks also tend to use lemon zest to add zing and flavor to many salads and dishes.

Lemon juice contains citric acid, which is really an organic acid.  All citrus fruits (like oranges, grapefruit, lemons, lime) contain this  acid.

An organic acid has the general formula R-COOH, where R could be a number of carbon and hydrogen atoms arranged as straight, branched or in a cyclic arrangement.  The COOH arrangement and the formula of citric acid are shown in the second picture.

As you can see, the formula is quite complicated.  However all organic acids have one or more of the -COOH or carboxyl group and are sometimes called carboxylic acids.

Let us start with simple organic acids.  When R=H, the formula of the organic acid is HCOOH and is called formic acid.   This is the acid found in ants!  The next acid in the series has R=  CHwhich is a methyl group and the formula is CH3COOH  and is called acetic acid.   This is the acid in vinegar and vinegar products like balsamic vinegar.  The more accurate IUPAC nomenclature (naming) of organic acids would use the name methanoic acid for formic acid and ethanoic acid for acetic acid.  The next acid in the series will have three carbon atoms and the carboxyl group and will be propanoic acid and so on.

But we need to look at common organic acids besides formic and acetic acid.  Mexicans and Indians are familiar with tamarind, used in cooking especially in Indian dishes.  This adds a tart taste to dishes and contains an acid called tartaric acid.  Milk contains the acid, lactic acid.  Most organic acids are weak acids, which means the acid is not completely ionized and the percentage of the hydronium ions present is low.  Just note that all organic acids have the characteristic COOH or carboxyl group present.

Remember methane as the first in the hydrocarbon series alkanes? Replace one of the hydrogens with the hydroxyl group OH and you get your first alcohol, methyl alcohol.  Unlike inorganic compounds where the presence of the hydroxyl group, OH, implies a base, the OH  here indicates alcohols.  The next in the series is ethyl alcohol, the familiar alcohol everyone imbibes.  None of the other alcohols in the series can be ingested.   An isomer of the next alcohol (propyl alcohol) is isopropyl alcohol and is familiarly known as rubbing alcohol used for medicinal purposes.  Methyl alcohol is also called wood alcohol and is used in many applications, but lately is found to be the best fuel for automobiles.(Ref.2)

Higher organic acids/carboxylic acids, like stearic acid are used in the manufacture of soaps.(Fig.3) Acetic acid is used in food and other acids are used as preservatives.  Acetic acid is also used in the manufacture of rayon.(Ref.3)(Fig4)

Activities for Middle School Teachers:

Let students go up to 12 carbons with a COOH group to write straight chain and branched chain organic acids.  Use the IUPAC name, (explained in Nuggets of Information).

Do the same with alcohols.

Note the number of isomers in each case. What kind of isomers do you obtain? ( Position of COOH/OH as well as cis-trans isomers and mirror image isomers)

As the number of carbon atoms increase are the acids liquids or solids?

Using ball and stick models or toothpicks, raisins and cherry tomatoes and marshmallows, construct the different isomers, say for a 5-carbon acid.

Nuggets of information:

The origin of the word ‘alcohol’ comes from Arabic which literally means al kuhl and refers to kohl/ antimony powder used with ethyl alcohol on the eyes.  Years later it was used to refer just to ethyl alcohol and in chemistry generally to all alcohols. (Ref.4)

Methyl alcohol has many names besides wood alcohol: wood spirit, hydroxy methane, Colonial spirit, Columbian spirit and also methanol. It has been used for embalming bodies by the ancient Egyptians.  The word ‘methyl’ was derived from Greek where ‘methy’ means wine and ‘hyle’ means wood or path of trees.  So people have been making illicit liquor using methyl alcohol for centuries. (Ref. 5,6)  Unfortunately, in many countries like India, people have died imbibing illicit liquor, because small amounts of methyl alcohol may not harm individuals but larger amounts leads to blindness, dizziness and even death.  Small amounts are already present in the fruits we eat. (Ref.7,8)

Part of the work of the International Union of Pure and Applied Chemistry or IUPAC is to set the rules for  the nomenclature of chemical compounds. So along with common names for organic acids and alcohols we have the standard IUPAC names as well. (Ref.9)

AHAs and BHAs are now very popular facial exfoliants.  AHA s are α-hydroxy acids like malic acid (from apples), tartaric acid ( from tamarind, grapes) and citric acid from citrus fruits) (Ref.10,11) (Figs. 2,4)  These AHAs are very popular for treating dermatological problems and have even been used for Fibromyalgia.  The only BHA or β-hydroxy acid used is salicylic acid. (Ref.12) which is a cyclic compound also called 2-hydroxy benzoic acid.  Salicylic acid is the active component in aspirin as well.

Oleic acid has been found in olive oil and has been considered to be  a good dietary supplement for people with diabetes. (Ref.13)(Fig.4)

Succinic Acid is a colorless crystalline solid, used in perfume making, medicine, manufacture of lacquers and in food production.It has two carboxylic -COOH groups and has 4 carbon atoms and is also called butanedioic acid (Ref.14)(Fig.3)

Maleic and Fumaric acids are cis and trans isomers,, have 4 carbons,also two carboxyl groups,-COOH,  but with a double bond each and can be manufactured starting with a derivative of succinic acid.  They are currently being used as food additives. (Ref.15,16) (Fig.3)

Butyric acid is produced when butter turns rancid.  It also has 4 carbons and is Butanoic acid, but with only one carboxyl group, -COOH. (Ref..17)(Fig.3)

Intense exercising can lead to lactic acidosis, which really means a high build up of lactic acid in the muscles.  This could lead to nausea and stomach pain, a temporary condition. (Ref.18)(Fig4).

Many times when people eat rich food, they talk about’acid reflux’.  This is probably the stomach walls producing more acid to digest all that food. Antacids, which are bases help neutralize the acid but maybe lemon juice everyday might be a better solution.  I end with more evidence that lemons are anti-bacterial, anti-viral and aid in digestion. (Ref.19)  Worth giving that a try, why not?








6.Blum, Deborah, Poisoner’s Handbook,(Penguin Press,2010)






























































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