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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 ...
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]
The hydrolysis of esters can occur through either acid and base catalyzed mechanisms, both of which proceed through a tetrahedral intermediate. In the base catalyzed mechanism the reactant goes from a neutral species to negatively charged intermediate in the rate determining (slow) step , while in the acid catalyzed mechanism a positively ...
Acid value – Milligrams of a base needed to neutralize 1 gram of a given acid; Amine value – Measure of an organic compound's nitrogen content; Bromine number – Mass of bromine absorbed by 100 grams of a given substance; EN 14214 – Fuel standard for biodiesel; Epoxy value – Measure of the epoxy content of a substance
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 conversion of methyl acetate back into its components, by an acid, is a first-order reaction with respect to the ester. The reaction of methyl acetate and a base, for example sodium hydroxide, is a second-order reaction with respect to both reactants. Methyl acetate is a Lewis base that forms 1:1 adducts with a variety of Lewis acids.
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.
For example, the pK a value of acetic acid is 4.8, while ethanol has a pK a of 16. Hence acetic acid is a much stronger acid than ethanol. This in turn means that for equimolar solutions of a carboxylic acid or an alcohol in water, the carboxylic acid would have a much lower pH. [1]: 263–7