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    WHO/Food Add./24.65
    FAO Nutrition Meetings
    Report Series No. 38A




    SPECIFICATIONS FOR IDENTITY AND 
    PURITY AND TOXICOLOGICAL EVALUATION 
    OF SOME ANTIMICROBIALS AND 
    ANTIOXIDANTS





    The content of this document is the result of the deliberations of the
    Joint FAO/WHO Expert Committee on Food Additives which met 8-17
    December 1964a





                   

    a Eighth Report of the Joint FAO/WHO Expert Committee on Food
    Additives, Wld Hlth Org. techn. Rep. Ser., 1965, 309; FAO
    Nutrition Meetings Report Series 1965, 38.


    THIODIPROPIONIC ACID

    CHEMICAL NAMES        3,3-thiodipropionic acid; ,'-thiodipropionic
                          acid; thiodihydracrylic acid; diethyl sulfide
                          2,2'-dicarboxylic acid

    EMPIRICAL FORMULA     C6H10O4S

    STRUCTURAL FORMULA

                          CH2 - CH2 - COOH
                          '
                          S
                          '
                          CH2 - CH2 - COOH


    MOLECULAR WEIGHT      178.21

    DEFINITION            Contains not less then 98.5% of C6H10O4S and
                          conforms to the following specifications.

    DESCRIPTION           Thiodipropionic acid is a white crystalline
                          solid having a slight characteristic odour.

    USE                   As an antioxidant for fats and other
                          foodstuffs.

    IDENTIFICATION

    A.  Solubility:       Water:     1 g is soluble in about 30 ml
                          Acetone:   Freely soluble
                          Ethanol:   Freely soluble

    B.  Melting range:  Between 130 and 134

    C.  Sulfur contents:  Between 17.5% and 18.5%

        Weigh 0.700 g of thiodipropionic acid and add 100 ml of acetic
        acid and 50 ml of ethanol and heat the mixture gently until the
        sample dissolves completely.  Add 3 ml of hydrochloric acid and
        4 drops of p-ethoxychrysoidin TS and immediately titrate with
        0.1 N bromide-bromate TS.  As the endpoint is approached (pink
        colour) add 4 more drops of the indicator solution and continue
        the titration dropwise, to a colour change from red to pale
        yellow.  Perform a blank determination and make any necessary
        correction. Each ml of 0.1 N bromide-bromate TS is equivalent to
        1.603 mg of S.

    PURITY TESTS

    Sulfated ash:  Not more than 0.2%.

    Heavy metals:  Not more than 10 mg/kg.

    Place 2 g, accurately weighed, in a porcelain crucible, add sufficient
    nitric acid to wet the sample, and ignite carefully at a low
    temperature until thoroughly charred, covering the crucible loosely
    with a porcelain lid during the ignition.  When carbonization is
    complete, add 2 ml of nitric acid and 5 drops of sulfuric acid, heat
    cautiously until white fumes are evolved and then ignite, preferably
    in a muffle furnace at 550  50C until the carbon is removed.  Cool,
    add 4 ml of diluted hydrochloric acid (1 in 2), cover, and digest on a
    steam bath for 15 minutes.  Remove the cover and evaporate on steam
    bath to dryness.  Moisten the residue with 0.05 ml of hydrochloric
    acid, add 10 ml of hot water and digest on a stem bath for 5 minutes.
    Filter, if necessary, add dilute to 25 ml.

    Arsenic:  Not more than 3 mg/kg.

    Selenium:  Not more than 30 mg/kg.

    Method

    Sample solution.  Transfer 2 g of thiodipropionic acid into a 250-ml
    conical flask and cautiously add 10 ml of 30% hydrogen peroxide. 
    After the initial reaction has subsided, add 6 ml of 70% perchloric
    acid and heat slowly until white fumes of perchloric acid are
    copiously evolved.  If the solution is brownish in colour due to the
    undecomposed organic matter, add a small portion of peroxide solution
    and heat again to white perchloric acid fumes, repeating if necessary
    until decomposition of the organic matter is complete and a colourless
    solution is obtained.  Cool, add 10 ml of water and filter the
    solution into a 200  25 mm test-tube.  Wash the filter until the
    filtrate measures 20 ml and add 20 ml of hydrochloric acid.

    Selenium stock solution.  Transfer 120.0 mg of metallic selenium
    (Se) into a 1000-ml volumetric flask, add 100 ml of dilute nitric acid
    (1 in 2), warm gently on a steam bath to effect the solution and
    dilute to volume with water.  Transfer 5.0 ml of this solution into a
    200-ml volumetric flask, dilute to volume with water and mix.  Each
    ml. of this solution contains 3 micrograms of selenium ion (Se).

    Standard solution.  On the day of use, transfer 20.0 ml of selenium
    stock solution (60 micrograms Se) into a 125-ml conical flask and add
    20 ml of hydrochloric acid.

    Procedure.  Place the test-tubes containing the standard solution
    and the sample solution in a water bath and heat until the temperature
    of the solution reaches 40.  To each tube add 400 mg of ascorbic
    acid, stir until dissolved and maintain both at 40 for 30 minutes. 

    Cool the solutions, dilute with water to 50 ml and mix. Any pink
    colour produced by the sample does not exceed that produced by the
    standard.

    ASSAY

    Weigh 0.350 g, dissolve in 40 ml of water, add phenolphthalein TS and
    titrate with 0.1 N sodium hydroxide to the first appearance of a
    faint pink colour that persists !or at least 30 seconds.  Each ml of
    0.1 N sodium hydroxide is equivalent to 8.910 mg of C6H10O4S.
    


    See Also:
       Toxicological Abbreviations
       THIODIPROPIONIC ACID (JECFA Evaluation)