Ethanol: Classification, Mechanism and Forensic Examination

Ethanol: Classification, Mechanism and Forensic Examination_ Forensic Yard (3)

The term ‘alcohol’ comes from the Arabic word “Al kohl” which means “something subtle”. Alcohol causes a slowing of nerve conduction which belongs to slower reaction times, difficulty in processing and integrating information.

Alcohol forms a homologous series beginning with methanol, ethanol, n-propanol, isopropanol, etc. The primary three are readily soluble in water altogether proportions but because the carbon chain length increases and water solubility decreases. Higher centers are depressed first followed by the midbrain and thalamus, spinal cord, and at last the medulla.

Forensic toxicologists play a major role in many facts of drunken driving particularly in measuring the pharmacological relationship between drug or alcohol use. They need an important role in analyzing samples from car drivers suspected of being diminished, interpreting results and presenting material evidence within the court.

Ethanol is the most typical alcohol in terms of drunken driving cases. Consumption of ethanol is legal in many authorities where it’s normally considered as socially acceptable if consumed in moderate quantity.

A diluted form of alcohol is absorbed slowly than the concentrated form. The kind of beverage also affects the speed of absorption. Whisky is absorbed rapidly and its complete absorption occurs within 1-3 hrs. The absorption of alcohol depends on the habituation and tolerance of the individual as habituated heavy drinkers tend to soak up alcohol quicker.

Section 85 of the Indian Penal Code says that nothing is an offense that is completed by someone who at the time of doing it, is by reason of intoxication, incapable of knowing the character of the act, or that he’s doing what’s either wrong or contrary to law; only if the thing which intoxicated him was administered to him without his knowledge or against his will. 

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Products of AlcoholAlcohol by Volume
Rum 50-60%
Whiskey, Gin, Brandy40-45%
Port, Sherry16-20%
Wine 10-15%
Beer4-8%
Arrack40-50%

Classification of Alcohols 

Alcohols are basically the hydroxy (-OH) derivatives of hydrocarbons. Broadly, they can be divided into three categories:

  1. Monohydroxy alcohols: This group of alcohols comprises only one hydroxyl (-OH) functional group. Examples are Methanol (Methyl Alcohol), Ethyl Alcohol (Ethanol), Isopropanol (Iso propyl alcohol), etc.
  2. Dihydroxy alcohols: This group of alcohols comprises two hydroxyl groups and is commonly referred to as Glycols. Examples are ethylene glycol, propylene glycol, etc.
  3. Trihydroxy alcohols: They are not true alcohols, but only derivatives. E.g., propane derivative is glycerol or glycerine.

Ethanol

Ethanol (Ethyl Alcohol) or Grain Alcohol is clear, colorless liquid with a classic fruity odor and having a burning taste. It is manufactured mostly by synthetic production from Ethylene. This is essentially done by a direct hydration process. It is soluble in water as well as lipid. The hydroxyl and ethyl groups confer both hydrophilic and lipophilic assets.

Thus, ethanol is an “amphophile”. Its specific gravity is 0.79. The ethanol content of various alcoholic beverages is expressed by volume percentage or by proof. It is toxic in many ways by oral, inhalation, subcutaneous, intravenous, intra-arterial and dermal routes. Vaporized ethanol can be quickly absorbed by breath leading to intoxication.

Ethanol is a CNS sedative but produces some apparently stimulating effects because of the depression of inhibitory control mechanisms in the brain. Several antihistaminic, multivitamin and cough syrups contain varying percentages of alcohol from 2 to 25%. It has been used in the past as an antiseptic.

Metabolism of Alcohols

 Alcohol is absorbed through the stomach and small intestine with effectively 100% of an oral dose absorbed in a healthy person. It transfers to the bloodstream which has its high water solubility content and is then distributed quickly throughout the body, distributing into all tissues.

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Alcohol is metabolized in the liver. Although the major pathway for metabolism is oxidation through acetaldehyde to Acetic Acid, a small percentage of Ethanol is conjugated to give Ethyl Glucuronide and Ethyl Sulphate.

Ethanol + NAD  🡪 Acetaldehyde + NADH

About 90% of the alcohol absorbed is oxidized in the liver and the rest 10% is excreted through urine and breathing. Alcohol is oxidized to Acetaldehyde by Alcohol Dehydrogenase (ADH) and coenzyme NAD in the liver.

This acetaldehyde is converted into free Acetic Acid. The acetate undergoes oxidation to Carbon Dioxide and water in the Krebs cycle. This Acetate can form Glycogen, proteins, fats and cholesterol. Alcohol can diffuse into free air and then can pass from the pulmonary system into the lungs where it is expelled through breath. This excretion of alcohol in breath makes breath-alcohol testing possible.

Mechanism of Action of Ethanol

Commonly, Ethanol is a Central Nervous System depressant. The mechanism by which alcohol affects cognition and psychomotor control is not understood completely. Alcohol produces instantaneous changes in many neurotransmitters and then increases the fluidity of cell membranes.

Alcohol in small doses interferes with cortical functions like conduct, judgment, and self-criticism but in larger doses, it depresses the medullary processes. Alcohol intoxication is also called Acute Alcohol Poisoning.

Forensic Examination for Ethanol 

 For the detection of ethanol, the following tests are to be carried out.

1. Iodoform Test

A suitable amount of the sample is taken and about 1 ml of 5% Sodium hydroxide solution is added to it and then iodine solution is added, drop-wise while shaking until the liquid becomes persistent dark brown in color. The solution is left for a few minutes.

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 If the Iodine color dissolves, more drops of iodine solution are added dropwise until the persistent brown color of iodine reappears. A few drops of dilute Sodium hydroxide solution are added to remove extra Iodine.

Equal volume of water is added and left for about ten minutes. Observation of Yellow crystalline precipitate indicates the positive test for the presence of Ethanol.

2. Dichromate Test

A suitable amount of sample is taken and about 0.2 ml of 2% Potassium dichromate solution is added followed by about 1 ml of concentrated Sulphuric Acid. The yellow color changes to green or blue which indicates the presence of Ethanol.

3. Sulphomolybdic Test

 Sulphomolybdic Acid is actually 1 gm of molybdic acid in 25 ml of concentrated sulphuric acid. Now for the detection, 2 ml of the hot component is added to 2 ml of the distillate.

A deep blue ring appears only once. On shaking, the whole mixture becomes deep blue. It indicates the presence of Ethyl Alcohol.

This test is highly sensitive. A strong solution of methyl alcohol gives only a light blue color after several minutes.

Conclusion

Absorption of alcohol is slower in the stomach than intestine where it is faster in an empty stomach than when it contains food. Food affects the absorption of alcohol by delaying the emptying time of the stomach. Fatty foods, Proteins and starch delay absorption of ethanol.

Food prevents 10-20% of the ingested alcohol from being absorbed. Alcohol abuse is widespread worldwide. Efforts have been made to prohibit alcohol consumption in many countries. However, such attempts usually lead to illicit consumption with even more serious consequences. 

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