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When oils and fats become rancid, triglycerides are converted into fatty acids and glycerol, causing an increase in acid value. [8] A similar situation is observed during aging of biodiesel through analogous oxidation and when subjected to prolonged high temperatures (ester thermolysis) or through exposure to acids or bases (acid/base ester ...
The conversion between hydroxyl value and other hydroxyl content measurements is obtained by multiplying the hydroxyl value by the factor 17/560. [2] The chemical substance may be a fat, oil, natural or synthetic ester, or other polyol. [3] ASTM D 1957 [4] and ASTM E222-10 [5] describe several versions of this method of determining hydroxyl value.
(The hydroxide solution used in such a titration is typically made from sodium hydroxide, potassium hydroxide, or barium hydroxide.) [1] It is measure of the steam volatile and water insoluble fatty acids, chiefly caprylic, capric and lauric acids, present in oil and fat. The value is named for the chemist who developed it, Eduard Polenske. [2]
The hydroxide anion adds to the carbonyl group of the ester. The immediate product is called an orthoester. Saponification part I. Expulsion of the alkoxide generates a carboxylic acid: Saponification part II. The alkoxide ion is a strong base so the proton is transferred from the carboxylic acid to the alkoxide ion, creating an alcohol:
The alcohols are obtained from the triglycerides (fatty acid triesters), which form the bulk of the oil. The process involves the transesterification of the triglycerides to give methyl esters which are then hydrogenated to produce the fatty alcohols. [4] Higher alcohols (C 20 –C 22) can be obtained from rapeseed oil or mustard seed oil.
Example of saponification reaction of a triglyceride molecule (left) with potassium hydroxide (KOH) yielding glycerol (purple) and salts of fatty acids ().. Saponification value or saponification number (SV or SN) represents the number of milligrams of potassium hydroxide (KOH) or sodium hydroxide (NaOH) required to saponify one gram of fat under the conditions specified.
An ester of a carboxylic acid.R stands for any group (typically hydrogen or organyl) and R ′ stands for any organyl group.. In chemistry, an ester is a compound derived from an acid (organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group (−OH) of that acid is replaced by an organyl group (R ′). [1]
In the food industry and biochemistry, interesterification (IE) is a process that rearranges the fatty acids of a fat product, typically a mixture of triglycerides.The process implies breaking and reforming the ester bonds C–O–C that connect the fatty acid chains to the glycerol hubs of the fat molecules.