Amine Structure & Synthesis
The preparation and properties of a homologous series of sodium salts of alkyl pentaerythritol ether sulfates, containing 12, 14, 16 and 18 carbon atoms are presented. The sodium salts of alkyl pentaerythritol ether sulfate, possessing two primary hydroxy groups and a sulfate group as hydrophilic portions, were prepared by sulfation of the corresponding alkyl pentaerythritol ethers obtained by the etherification reaction of pentaerythritol with alkyl bromide.
These surfactants showed excellent properties in aqueous solution such as lower cmc, higher stability toward calcium ions and low Krafft points. They were noted to function as highly effective calcium soap dispersing agents.
Our last topic for today is the synthesis of amines
Amphoteric (or zwitterionic) surfactants are so called because the head-group carries both a negative and positive charge. A range of methods is used to produce such materials, almost all of which contain a quaternary ammonium ion (a cation). The negatively charged group can be carboxylate, -CO2-, sulfate, -OSO3- or sulfonate, -SO3-. One such well-used class is the alkyl betaines which have a carboxyl group. A long-chain carboxylic acid reacts with a diamine to form a tertiary amine. On further reaction with sodium chloroethanoate, a quaternary salt is formed:
The glycerides used to make surfactants contain saturated and unsaturated carboxylic acids which have an even number of carbon atoms, generally within the range 12-20, for example, octadecanoic acid (stearic acid), CH3(CH2)16CO2H.
Synthetic surfactants have one very important advantage over soaps. Because soaps form insoluble calcium and magnesium salts with the calcium and magnesium ions in hard water and in the clays which are present in dirt, much of the soap is wasted forming an insoluble scum. However, this is avoided when using a synthetic surfactant. For example, in the anionic surfactants, the carboxylate group in soap is replaced by a sulfonate or sulfate group as the hydrophilic component. The corresponding calcium and magnesium salts are more soluble in water than the calcium and magnesium salts of carboxylic acids.
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These formulations contain between 13-40% of surfactants which are predominantly alkyl ether sulfates but also include nonionics and amphoterics (betaines).
Synthesis of Radiolabeled Compounds
More widely used than simple alkyl sulfates are various types of sodium alkyl ether sulfates (SLES).
In the manfacture of SLES the primary alkyl alcohol (from a synthetic or natural source and typically a blend based around dodecanol) is first ethoxylated with 1 to 3 molar equivalents of (as described below for the manufacture of nonionic surfactants). The product is then sulfated using sulfur trioxide and neutralized with alkali to form the alkyl ether sulfate:
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Many detergent products, particularly liquids, contain other synthetic anionic surfactants such as alkyl sulfates, esters of linear alcohols (C10-C18) and sulfuric acid. The alkyl sulfates are also used in personal care products such as toothpaste and are manufactured by treating the alcohol with sulfur trioxide. The product is then neutralised with aqueous sodium hydroxide solution to form a sodium alkyl sulfate:
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The alkylate is sulfonated using an air/sulfur trioxide mixture, and the resulting sulfonic acid is then neutralised with an aqueous solution of sodium hydroxide (often in situ), for example:
General & Introductory Chemistry
Simple alcohols and phenols may be alkylated using dimethyl sulfate in slightly hydrated solid/liquid heterogeneous media with 1,4-dioxane or triglyme/potassium hydroxide and small amounts of water to give the corresponding methyl ethers in excellent yield. For example, -butyl alcohol is converted to -butyl methyl ether in nearly quantitative yield (eq 3).