Methylamine hydrochloride can be identified using both chemical and instrumental methods. Below are the main techniques:
1. Physical and Simple Observations
a. Odor:
Free methylamine has a very strong, fishy or ammonia-like odor.
The hydrochloride salt form has a significantly milder smell.
b. Solubility:
Freely soluble in water, forming a mildly acidic solution due to the chloride ion.
2. Chemical Tests
a. Basicity Test:
Mix an aqueous solution of methylamine hydrochloride with sodium hydroxide (NaOH). Methylamine gas is released:
CH3NH3Cl+NaOH→CH3NH2(g)+NaCl+H2OCH_3NH_3Cl + NaOH \rightarrow CH_3NH_2 (g) + NaCl + H_2OCH3NH3Cl+NaOH→CH3NH2(g)+NaCl+H2O
The released gas turns red litmus paper blue, indicating a basic compound.
b. Nitrous Acid Test (for primary amines):
Reacts with nitrous acid (generated in situ from NaNO₂ and HCl) to produce nitrogen gas:
CH3NH2+HNO2→CH3OH+N2(g)+H2OCH_3NH_2 + HNO_2 \rightarrow CH_3OH + N_2 (g) + H_2OCH3NH2+HNO2→CH3OH+N2(g)+H2O
Effervescence (bubbling) due to nitrogen gas is a positive result for a primary amine.
3. Instrumental Methods
a. FT-IR Spectroscopy:
N–H stretching bands appear around 3300–3400 cm⁻¹ (usually as a weak doublet).
C–N stretching bands occur between 1020–1250 cm⁻¹.
The chloride ion itself is not IR-active but the salt nature influences the spectrum.
b. Proton NMR (¹H-NMR):
Methyl protons (CH₃) appear in the 2.2–2.8 ppm range.
Amine protons (NH₂⁺ or NH₃⁺) usually show broad signals in the 1–4 ppm region, depending on solvent and pH.
Due to the salt form, NH₃⁺ protons may appear as broad or shifted peaks.
c. GC-MS (after basification):
Free methylamine (liberated by treatment with NaOH) can be analyzed using GC-MS.
Molecular weight of methylamine: 31 g/mol.
The mass spectrum will show a base peak corresponding to the CH₃NH₂ molecular ion.
1. Physical and Simple Observations
a. Odor:
Free methylamine has a very strong, fishy or ammonia-like odor.
The hydrochloride salt form has a significantly milder smell.
b. Solubility:
Freely soluble in water, forming a mildly acidic solution due to the chloride ion.
2. Chemical Tests
a. Basicity Test:
Mix an aqueous solution of methylamine hydrochloride with sodium hydroxide (NaOH). Methylamine gas is released:
CH3NH3Cl+NaOH→CH3NH2(g)+NaCl+H2OCH_3NH_3Cl + NaOH \rightarrow CH_3NH_2 (g) + NaCl + H_2OCH3NH3Cl+NaOH→CH3NH2(g)+NaCl+H2O
The released gas turns red litmus paper blue, indicating a basic compound.
b. Nitrous Acid Test (for primary amines):
Reacts with nitrous acid (generated in situ from NaNO₂ and HCl) to produce nitrogen gas:
CH3NH2+HNO2→CH3OH+N2(g)+H2OCH_3NH_2 + HNO_2 \rightarrow CH_3OH + N_2 (g) + H_2OCH3NH2+HNO2→CH3OH+N2(g)+H2O
Effervescence (bubbling) due to nitrogen gas is a positive result for a primary amine.
3. Instrumental Methods
a. FT-IR Spectroscopy:
N–H stretching bands appear around 3300–3400 cm⁻¹ (usually as a weak doublet).
C–N stretching bands occur between 1020–1250 cm⁻¹.
The chloride ion itself is not IR-active but the salt nature influences the spectrum.
b. Proton NMR (¹H-NMR):
Methyl protons (CH₃) appear in the 2.2–2.8 ppm range.
Amine protons (NH₂⁺ or NH₃⁺) usually show broad signals in the 1–4 ppm region, depending on solvent and pH.
Due to the salt form, NH₃⁺ protons may appear as broad or shifted peaks.
c. GC-MS (after basification):
Free methylamine (liberated by treatment with NaOH) can be analyzed using GC-MS.
Molecular weight of methylamine: 31 g/mol.
The mass spectrum will show a base peak corresponding to the CH₃NH₂ molecular ion.
