Methylparaben, also methyl paraben, one of the parabens, is a preservative with the chemical formula CH3(C6H4(OH)COO). It is the methyl ester of p-hydroxybenzoic acid. It is also used as a food preservative and has the E number E218.

Specifications of Methylparaben USP NF Grade

C8H8O3 --- 152.15
Benzoic acid, 4-hydroxy-, methyl ester.
Methyl p-hydroxybenzoate --- 99-76-3.
Methylparaben contains not less than 98 percent and not more than 102 percent of C8H8O3.

Packaging and storage: Preserve in well-closed containers.
Identification:
A: Infrared Absorption.
B: Melting range: between 125 and 128.
Color of solution: Dissolve 1 g in alcohol, dilute with alcohol to 10 mL, and mix (Methylparaben solution). This solution is clear and not more intensely colored than alcohol or a solution prepared immediately before use by mixing 2.4 mL of ferric chloride, 1.0 mL of cobaltous chloride and 0.4 mL of cupric sulfate with 0.3 N hydrochloric acid to make 10 mL and diluting 5 mL of this solution with 0.3 N hydrochloric acid to make 100 mL. Make the comparison by viewing the solutions downward in matched color-comparison tubes against a white surface.
Acidity: To 2 mL of Methylparaben solution prepared in the Color of solution test add 3 mL of alcohol, 5 mL of carbon dioxide-free water and 0.1 mL of bromocresol green and titrate with 0.10 N sodium hydroxide: not more than 0.1 mL is required to produce a blue color.
Residue on ignition: not more than 0.1%, determined on 1.0 g.
Related substances: To pass the test.
Assay: To about 1.000 g of Methylparaben, accurately weighed, add 20.0 mL of 1 N sodium hydroxide and heat at about 70C for 1 hour. Cool rapidly in an ice bath. Carry out the titration on the solutions at room temperature. Titrate the excess sodium hydroxide with 1 N sulfuric acid, continuing the titration until the second point of inflection and determining the endpoint potentiometrically. Perform a blank determination. Each mL of 1 N sodium hydroxide is equivalent to 152.1 mg of C8H8O3.

Methyl Hydroxybenzoate BP Grade

Methylparaben
Methyl Parahydroxybenzoate, Ph Eur
C8H8O3 --- 152.1 --- 99-763-3
Action and use: Antimicrobial preservative.

DEFINITION
Methyl 4-hydroxybenzoate.
Content: 98.0 per cent to 102.0 per cent.

CHARACTERS
Appearance: White or almost white, crystalline powder or colourless crystals.
Solubility: Very slightly soluble in water, freely soluble in alcohol and in methanol.

IDENTIFICATION
First identification A, B.
Second identification A, C, D.
A. Melting point: 125C to 128C.
B. Infrared absorption spectrophotometry. Comparison methyl parahydroxybenzoate CRS.
C. Examine the chromatograms obtained in the test for related substances.
Results: The principal spot in the chromatogram obtained with test solution (b) is similar in position and size to the principal spot in the chromatogram obtained with reference solution (b).
D. To about 10 mg in a test-tube add 1 ml of sodium carbonate solution, boil for 30 s and cool (solution A). To a further 10 mg in a similar test-tube add 1 ml of sodium carbonate solution; the substance partly dissolves (solution B). Add at the same time to solution A and solution B 5 ml of aminopyrazolone solution and 1 ml of potassium ferricyanide solution and mix. Solution B is yellow to orange-brown. Solution A is orange to red, the colour being clearly more intense than any similar colour which may be obtained with solution B.

TESTS
Solution S: Dissolve 1.0 g in alcohol and dilute to 10 ml with the same solvent.
Appearance of solution: Solution S is clear and not more intensely coloured than reference solution.
Acidity: To 2 ml of solution S add 3 ml of alcohol, 5 ml of carbon dioxide-free water and 0.1 ml of bromocresol green solution. Not more than 0.1 ml of 0.1 M sodium hydroxide is required to change the colour of the indicator to blue.
Related substances: To pass the test (0.5 per cent).
Sulphated ash: Maximum 0.1 per cent, determined on 1.0 g.

ASSAY
To 1.000 g add 20.0 ml of 1 M sodium hydroxide. Heat at about 70C for 1 h. Cool rapidly in an ice bath. Prepare a blank in the same manner. Carry out the titration on the solutions at room temperature. Titrate the excess sodium hydroxide with 0.5 M sulphuric acid , continuing the titration until the second point of inflexion and determining the end-point potentiometrically.
1 ml of 1 M sodium hydroxide is equivalent to 152.1 mg of C8H8O3.

IMPURITIES
A. R = H: 4-hydroxybenzoic acid,
B. R = CH2-CH3: ethyl 4-hydroxybenzoate,
C. R = CH2-CH2-CH3: propyl 4-hydroxybenzoate,
D. R = CH2-CH2-CH2-CH3: butyl 4-hydroxybenzoate.

Specifications of Methylparaben FCC Food Grade

Methyl p-Hydroxybenzoate
HO COOCH3
C8H8O3 --- Formula weight: 152.15
INS: 218 CAS: 99-76-3

DESCRIPTION
Methylparaben occurs as small, colorless crystals or as a white, crystalline powder. One gram dissolves in about 400 mL of water at 25C, in about 50 mL of water at 80C, in about 2.5 mL of alcohol, in about 7 mL of ether, and in about 4 mL of propylene glycol. It is slightly soluble in glycerin and in fixed oils.
Function: Preservative; antimicrobial agent.

REQUIREMENTS
Identification: Dissolve 500 mg of sample in 10 mL of 1 N sodium hydroxide, boil for 30 min, allow the solution to evaporate to a volume of about 5 mL, and cool. Acidify the solution with 2 N sulfuric acid, collect the crystals on a filter, wash several times with small portions of water, and dry in a desiccator over silica gel. The p-hydroxybenzoic acid so obtained melts between 212C and 217C.
Assay: Not less than 99.0% and not more than 100.5% of C8H8O3, calculated on the dried basis.
Acidity: Passes test.
Lead: Not more than 2 mg/kg.
Loss on Drying: Not more than 0.5%.
Melting Range: Between 125° and 128°.
Residue on Ignition: Not more than 0.05%.