Iodine values

The iodine number (iodine value) test method (ASTM D-2078, IP 84) is included in some specifications and is a measure of fatty acid components or unsaturation either as olefins and/or aromatics. The former are very unUkely to be present in any oil that has undergone sufficient refining to make it colorless, whereas the aromatic content can be controlled by setting a suitable value for the ultraviolet absorption. 

In the test method (ASTM D-2078), a sample is dissolved in chloroform and reacted with Wijs solution for 30 min in the dark at 25°C. At the end of the reaction, the solution is mixed with potassium iodide (KI) and titrated with sodium thiosulfate and starch indicator and compared to a blank determination. 

The bromine number is the number of grams of bromine that will react with 100 g of the sample under the test conditions and is better suited to the determination of unsaturated constituents in oil (ASTM D-875, ASTM D-1159, ASTM D-2710, IP 130). The magnitude of the bromine number is used as a measure of aliphatic unsaturation in petroleum products. In the test, a known weight of the sample dissolved in a specified solvent maintained at 0-5°C (32-41 °F) is titrated with standard bromide-bromate solution. Determination of the end point is method dependent. 

Oils and fats, both animal and vegetable, are mixtures of mixed glycerides represented by the general formula 

CH=CHCH2CH=CH-CH2CH=CH(CH2)7-C00H Linolenic Acid 

The combinations having predominance of short-chain saturated fatty acids or long chain fatty acids with a considerable degree of unsaturation are liquids at ordinary temperatures and are called oils while others, that are solids at ordinary temperatures, are known as fats. 

The degree of unsaturation of oils and fats is reported in terms of their Iodine Number or Iodine Value. (I.V.) which is the number of grams of Iodine equivalent to the amount of Iodine Monochloride (ICl) absorbed by 100 g of the oil. 

Each oil has its own characteristic iodine value (varying between narrow limits), and so the determination of iodine value can be utilised to detect and even to determine (though approximately) the extent of contamination in any specific oil. 

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Fat or oil Solidification point, °C Specific gravity (15°C/15°C) Refractive index Acid value Saponification value Iodine value... 

Refractive index Acid value Saponification value Iodine value... 

Infrared spectra of fats and oils are similar regardless of their composition. The principal absorption seen is the carbonyl stretching peak which is virtually identical for all triglyceride oils. The most common appHcation of infrared spectroscopy is the determination of trans fatty acids occurring in a partially hydrogenated fat (58,59). Absorption at 965 - 975 cm is unique to the trans functionaHty. Near infrared spectroscopy has been utilized for simultaneous quantitation of fat, protein, and moisture in grain samples (60). The technique has also been reported to be useful for instmmental determination of iodine value (61). 

Measurement of Unsaturation. The presence of double bonds in a fatty acid side chain can be detected chemically or through use of instmmentation. Iodine value (IV) (74) is a measure of extent of the reaction of iodine with double bonds the higher the IV, the more unsaturated the oil. IV may also be calculated from fatty acid composition. The cis—trans configuration of double bonds may be deterrnined by infrared (59) or nmr spectroscopy. Naturally occurring oils have methylene-intermpted double bonds that do not absorb in the uv however, conjugated dienes maybe deterrnined in an appropriate solvent at 233 nm. 

Iodine monochloride [7790-99-0] ICl, mol wt 162.38, 78.16% I, is a black crystalline soHd or a reddish brown Hquid. SoHd ICl exists ia two crystalline modifications the a-form, as stable mby-red needles, d = 3.86 g/mL and mp 27.3°C and as metastable brownish red platelets, d = 3.66 g/mL, mp 13.9°C and bp 100°C (dec). Iodine monochloride is used as a halogenation catalyst and as an analytical reagent (Wij s solution) to determine iodine values of fats and oils (see Fats and fatty oils). ICl is prepared by direct reaction of iodine and Hquid chlorine. Aqueous solutions ate obtained by treating a suspension of iodine ia moderately strong hydrochloric acid with chlorine gas or iodic acid (118,119). 

To analy2e fatty amines, both wet and instmmental methods of analysis are used. Wet methods routinely used are total amine value (ASTM Method D2073) combining weight or neutralization equivalent primary, secondary, and tertiary amine content (ASTM Method D2083) moisture, Kad-Fischer (ASTM Method D2072) and iodine value, measure of unsaturation (ASTM Method D2075). These provide important information on physical and chemical characteristics of the amine products used in various appHcation areas (8,76,81). In addition to the ASTM methods available, the American Oil Chemists Society has developed methods of analysis for fatty amines (82). 

There are no universally accepted wet analytical methods for the characteri2ation of quaternary ammonium compounds. The American Oil Chemists Society (AOCS) has estabhshed, however, a number of appHcable tests (180). These include sampling, color, moisture, amine value, ash, iodine value, average molecular weight, pH, and flash point. 

The quahty of sulfonic acids produced as iatermediates on an iadustrial scale is important to detergent manufacturers. Parameters such as color, water, free oil (unsulfonated material), and acid value (actual sulfonic acid) are all factors that determine the quaUty of a sulfonic acid. The quaUty of the feedstock prior to sulfonation, such as iodine value, water content, and sulfonatabiUty, affects the quaUty of the sulfonic acid produced. Sulfonation conditions, such as temperature, molar ratio, rate, etc, also affect the quaUty of sulfonic acid. 

An important chemical characteristic of unsaturated acids is the iodine value (IV), which indicates the average degree of unsaturation. It is equal to the number of grams of iodine absorbed under standard conditions by 100 g of the unsaturated acid. 

Includes palm kernel and babassu. IV = Iodine value. 

The determination of iodine value (IV), AOCS Tg 1-64, is sometimes used to determine the extent of unsaturation. Because the tertiary aUyflc hydrogen ia the compounds is capable of substitution by halogen atoms, this only approximates a value for the degree of unsaturation. 

The composition of an oil and the progress of its hydrogenation is expressed in terms of its iodine value (IV). Edible oils are mixtures of unsaturated compounds with molecular weights in the vicinity of 300. The IV is a measure of this unsaturation. It is found by a standardized procedure. A solution of ICl in a mixture of acetic acid and carbon tetrachloride is mixed in with the oil and allowed to reac t to completion, usually for less than I h. Halogen addition takes place at the double bond, after which the amount of unreacted iodine is determined by analysis. The reaction is... 

TABLE 23-13 Time/ Temperature/ and Iodine Value of Tallow Hydrogenation ... 

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