Sodium Metal Lucas and Esterification Tests for Alcoholic Group with Reactions and Observations
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. Ethanol is one of the common alcohols. It is present in the drugs and is the main component of alcoholic drinks. Alcohol denotes an entire class of compounds of which methanol and ethanol are the primary members. The higher alcohols and the primary alcohols are expressed generally with the formula CnH2n+1OH.
The primary, secondary, and tertiary alcohol is included as the simplest mono alcohol that is the prime subject of the article. Here, 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 tests to detect the alcoholic group present-
Ester test
Sodium metal test
Ceric ammonium nitrate test
Acetyl chloride test
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-colored 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.
The chemical reactions are given below.
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Materials Required
Sodium metal
Acetic acid
Ceric ammonium nitrate
Acetyl chloride
Ammonium hydroxide
Iodine
Sodium hydroxide
Calcium sulfate
Lucas reagent (zinc chloride and Con.HCl)
Test tubes
Test tube holder
Filler
Procedure and Observations (Identification Test for 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 on Test for Alcoholic Functional Group in Alcohols
1. What is the test for alcoholic group in organic chemistry?
The test for alcoholic group is a qualitative analysis used to identify the presence of a –OH (hydroxyl) group attached to a saturated carbon atom in an alcohol. Common laboratory tests include:
- Sodium metal test – alcohol reacts with sodium to form alkoxide and hydrogen gas.
- Lucas test – distinguishes primary, secondary, and tertiary alcohols.
- Oxidation test – uses acidified potassium dichromate to detect oxidizable alcohols.
- Ester test – alcohol forms a fruity-smelling ester with a carboxylic acid.
2. How does sodium metal test confirm the presence of an alcohol?
The sodium metal test confirms an alcohol by producing hydrogen gas when sodium reacts with the –OH group. The general reaction is:
2ROH + 2Na → 2RONa + H2(g)
- ROH = alcohol
- RONa = sodium alkoxide
- Effervescence due to H2 gas indicates presence of –OH group
3. What is Lucas test for alcoholic group?
The Lucas test is used to classify alcohols as primary, secondary, or tertiary based on their reaction with Lucas reagent (conc. HCl + anhydrous ZnCl2). The reaction forms an alkyl chloride:
ROH + HCl → RCl + H2O
- Tertiary alcohol: immediate turbidity.
- Secondary alcohol: turbidity in 5–10 minutes.
- Primary alcohol: no turbidity at room temperature.
4. What is the oxidation test for alcohols?
The oxidation test for alcohols uses acidified potassium dichromate (K2Cr2O7/H2SO4) to detect oxidizable alcohols by a color change from orange to green. Typical reactions include:
- Primary alcohol: oxidized to aldehyde, then to carboxylic acid.
- Secondary alcohol: oxidized to ketone.
- Tertiary alcohol: no reaction under mild conditions.
5. How can you distinguish primary, secondary, and tertiary alcohols?
Primary, secondary, and tertiary alcohols can be distinguished using the Lucas test and oxidation reactions. Key differences are:
- Primary (1°): slow Lucas reaction; oxidized to aldehyde/carboxylic acid.
- Secondary (2°): moderate Lucas reaction; oxidized to ketone.
- Tertiary (3°): immediate Lucas reaction; resistant to oxidation.
6. What is the ester test for alcoholic group?
The ester test confirms an alcohol by producing a fruity-smelling ester when heated with a carboxylic acid in presence of concentrated H2SO4. A typical reaction is:
CH3COOH + C2H5OH ⇌ CH3COOC2H5 + H2O
- Conc. H2SO4 acts as a catalyst and dehydrating agent.
- The sweet fruity smell indicates ester formation.
7. Why do alcohols react with sodium but not with NaOH?
Alcohols react with sodium metal because the –OH hydrogen is weakly acidic, but they generally do not react with NaOH due to insufficient acidity. In the sodium reaction:
2ROH + 2Na → 2RONa + H2(g)
- Sodium is highly reactive and displaces hydrogen.
- Alcohols are less acidic than water.
- NaOH is not strong enough to deprotonate most alcohols.
8. What is the ceric ammonium nitrate test for alcohols?
The ceric ammonium nitrate test detects alcohols by producing a red or orange-red complex with (NH4)2Ce(NO3)6. Key points include:
- Formation of colored complex indicates presence of –OH group.
- Works best for aliphatic alcohols.
- Used as a quick qualitative confirmation test.
9. Can phenols give the same test as alcohols?
Phenols do not behave exactly like alcohols because the –OH group in phenols is attached to an aromatic ring, which changes its reactivity. Differences include:
- Phenols are more acidic than alcohols.
- Phenols react with NaOH to form phenoxide ions.
- Lucas test is generally negative for phenols.
10. What precautions should be taken while performing tests for alcoholic group?
Proper safety precautions are essential while performing qualitative tests for alcoholic group. Important precautions include:
- Handle sodium metal with dry forceps and keep away from water.
- Use concentrated H2SO4 carefully to avoid burns.
- Perform heating reactions in a water bath, not over direct flame.
- Work in a well-ventilated area to avoid inhaling fumes.
