Test for Alcoholic Group

Alcohols

In organic chemistry, functional groups play a crucial role. Alcohols are referred to as the organic compound with -OH functional group. Compounds containing a -OH group bonded to a tetrahedral carbon atom are alcohols. For alcohol, the general formula is R-OH, where R consists of an alkyl group. In this article, we will study the identification test for alcohol.


Qualitative Test For Alcohol:


Aim

To identify the present functional group (test for Alcoholic group)  in a given organic compound.


Theory 

Qualitative test for alcohol- there are various test to detect the alcoholic group present-

  1. Ester test

  2. Sodium metal test

  3. Ceric ammonium nitrate test

  4. Acetyl chloride test

  5. Iodoform test


Ester Test

Carboxylic acids react with alcohols resulting in the formation of fruit-smelling ester. The reaction is called the esterification reaction between an alcohol and a carboxylic acid. This reaction is a concentrated sulphuric acid-catalyzed reaction.

R-OH + R-COOH → R-COOR + H2O

CH3OH + CH3-COOH → CH3-COOCH3 + H2O


Sodium Metal Test

It is based on the appearance of brisk effervescence when alcohol reacts with active metals such as sodium because of the release of hydrogen gas

Below, the chemical reaction is given.

2R-OH + 2Na → 2R-O-Na + H2

2CH3-OH + 2Na → 2CH3-O-Na + H2


Ceric Ammonium Nitrate Test for Alcohol

Due to the formation of a complex compound and ammonium nitrate, alcohol or ceric ammonium nitrate reactions form a pink or red-coloured precipitate.

(NH4)2 [Ce(NO3)6] + 3ROH → [Ce(NO3)4(ROH)3] + 2NH4NO3

(NH4)2 [Ce(NO3)6] + 3CH3OH → [Ce(NO3)4(CH3OH)3] + 2NH4NO3

The formation of ester and hydrogen chloride results from alcohol reactions with acetyl chloride

R-OH + CH3-CO-Cl → CH3-COOR + HCl

HCl + NH4OH → NH4Cl + H2O


Iodoform

This test is conducted with secondary alcohols, acetaldehyde, and ketones. The compound is heated in the presence of a sodium hydroxide solution and iodine. The presence of alcohol is shown by the formation of a yellow iodoform precipitate.

CH3-CH(OH)-CH3 + I2 + 2NaOH → CH3-CO-CH3 + 2NaI + 2H2O

CH3-CO-CH3 + 3I2 + 4NaOH → CHI3(Iodoform) + CH3COONa + 3NaI + 3H2O


Luca’s Test

This test is used to distinguish between primary, secondary, and tertiary alcohols. Lucas reagent is a mixture of concentrated hydrochloric acid and zinc chloride. Tertiary alcohols on treatment with Luca’s reagent result in the formation of white ppt immediately. Secondary alcohol on treatment with Lucas reagent forms white ppt after 5 minutes. Primary alcohol on treatment with Luca’s reagent does not form white ppt at room temperature.


Materials Required 

  1. Sodium metal

  2. Acetic acid

  3. Ceric ammonium nitrate

  4. Acetyl chloride

  5. Ammonium hydroxide

  6. Iodine

  7. Sodium hydroxide

  8. Calcium sulfate

  9. Lucas reagent (zinc chloride and Con.HCl)

  10. Test tubes

  11. Test tube holder

  12. Filler


Procedure and Observations (Identification Test for Alcohol)

Tests

Procedure 

Observation

1.Ester Test

1. In a clean, dry test tube, take 1ml of the organic liquid to be tested. 

2. Add 1 ml of glacial acetic acid and 2-3 drops of concentrated sulfuric acid.

3. For 10 minutes, heat the mixture in a water bath. 

4. The hot mixture is poured into a cold water-containing beaker. 

5. In the beaker, smell the water. 

6. The alcoholic group's existence is confirmed by a fruity scent

Fruity smell indicates the presence of the alcoholic group.

2.Sodium Metal Test


1. Take the organic compound into a dry test tube to be tested. 

2. To remove excess water, add 1gm of anhydrous calcium sulfate and shake well. 

3. To another clean test tube, decant the solution. 

4. Add a small piece of sodium metal.  

5. If brisk effervescence appears due to the evolution of hydrogen gas indicate the presence of the alcoholic group.

Release of Brisk effervescence

3.Ceric Ammonium Nitrate Test


1. In a dry test tube, take 1ml of the given compound. 

2. Add a few drops of ceric ammonium nitrate and shake the solution well. 

3. Observe the solution. 

4. If red precipitate occurs, it conforms to the involvement of the alcoholic group.

The appearance of wine red colour precipitate

4. Acetyl Chloride Test


1. In a clean test tube, take 2ml of the organic compound given 

2. Add 1gm of sulfate of anhydrous calcium and shake well. 

3. Solution Filtering. Add 3 to 4 drops of acetyl chloride to the filtrate, then shake well. 

4. Take a rod of a glass dipped in a solution of ammonium hydroxide. 

5. Put the glass rod next to the mouth of the test tube. 

6. The involvement of the alcoholic party is changed if white fumes occur.

White fumes formation

5.Iodoform Test


1. In a clean, dry test tube, take 1ml of the given organic compound. 

2. Add 1ml of 1 percent solution of iodine to it.

3. Add dilute sodium hydroxide solution dropwise until the brown colour of iodine is discharged.

4. In a water bath, heat the mixture gently. 

5. The presence of either ethonal or acetaldehyde or methyl ketone is suggested by the formation of yellow precipitates.

Yellow precipitate formation.


Results

The given organic compound is ___________. (primary alcohol, secondary alcohol or tertiary alcohol)


Precautions

  • Sodium metal should be carefully treated, as it responds violently to water. 

  • As it can cause nasal irritation, iodine should not be inhaled.

Did you Know?

The boiling points of alcohols of equal molecular weights are much higher than those of alkanes. Ethanol, for example, has a boiling point of 78 °C (173 °F) with a molecular weight (MW) of 46, while propane (MW 44) has a boiling point of −42 °C (−44 °F). Such a large difference in boiling points means that ethanol molecules are much more highly attracted to each other than propane molecules are. The ability of ethanol and other alcohols to form intermolecular hydrogen bonds results in much of this disparity. (For a discussion of hydrogen bonding, see chemical bonding: Intermolecular forces.)

FAQs (Frequently Asked Questions)

Question 1: Which Alcohol is Used in Sanitisers?

Answer: This allows the protective coatings of microbes to be lost and become non-functional. Formulations containing 80% ethanol (percent volume/volume) or 75% isopropyl alcohol are recommended by the Center for Disease Control and Prevention, but sanitisers containing 60 to 95% alcohol are generally appropriate.

Question 2: Which is Better Ethanol or Isopropyl Alcohol?

Answer: Findings from studies have shown that the disinfection of isopropyl alcohol was more effective than that of ethanol. Since ethanol requires more time and complex procedures to act, it should be easier to use disinfectants that act faster and simpler, such as isopropyl alcohol.

Question 3: Are Alcohols Acidic or Basic?

Answer: By the Arrhenius concept of acid and base, when dissolved in water, alcohol is neither acidic nor basic, as it neither produces H+ nor OH- in the solution. Generally, they are weak acids. Brønsted acids with pKa values normally in the range of 15-20 are very weak alcohols.