- Chemistry in everyday life – 02
- TYPES OF SOAPS
- SYNTHETIC DETERGENTS
DICHLOROMETHANE (METHYLENE CHLORIDE)
Chemistry in everyday life – 02
- Food preservatives prevent spoilage of food due to microbial growth. The most commonly used preservatives include Table Salt, Sugar, Vegetable Oils and Sodium Benzoate,
- . SODIUM BENZOATE is used in limited quantities and is metabolized in the body. Salts of sorbic acid and propanoic acid are also used as preservatives.
- SOAPS ARE THE DETERGENTS used since long. Soaps used for cleaning purpose are sodium or potassium salts of long chain fatty acids, e.g., Stearic, Oleic and Palmitic Acids. Soaps containing sodium salts are formed by heating fat (i.e., glyceryl ester of fatty acid) with aqueous sodium hydroxide solution. This reaction is KNOWN AS SAPONIFICATION.
- In this reaction, esters of fatty acids are hydrolyzed, and the soap obtained remains in colloidal form. It is precipitated from the solution by adding sodium chloride. The solution left after removing the soap contains glycerol, which can be recovered by fractional distillation.
- Only sodium and potassium soaps are soluble in water and are used for cleaning purposes. Generally, potassium soaps are soft to the skin than sodium soaps. These can be prepared by using potassium hydroxide solution in place of sodium hydroxide.
- Basically, all soaps are made by boiling fats or oils with suitable soluble hydroxide. Variations are made by using different raw materials.
- TOILET SOAPS are prepared by using better grades of fats and oils and care is taken to remove excess alkali. COLOUR AND PERFUMES are added to make these more attractive.
- Soaps that float in water are made by beating tiny air bubbles before their hardening.
- Transparent soaps are made by dissolving the soap in ethanol and then evaporating the excess solvent.
- In medicated soaps, substances of medicinal value are added. Shaving soaps contain glycerol to prevent rapid drying. A gum called; rosin is added while making them. It forms SODIUM ROSINATE which lathers well. LAUNDRY SOAPS contain fillers like SODIUM ROSINATE, SODIUM SILICATE, BORAX AND SODIUM CARBONATE.
- HARD WATER CONTAINS CALCIUM AND MAGNESIUM IONS. These ions form insoluble calcium and magnesium soaps respectively when sodium or potassium soaps are dissolved in hard water.
- These insoluble soaps separate as scum in water and are useless as cleansing agent. In fact, these are hinderance to good washing, because the precipitate adheres onto the fibre of the cloth as gummy mass. Hair washed with hard water looks dull because of this ‘ sticky precipitate. Dye does not absorb evenly on cloth washed with soap using hard water, because of this gummy mass.
- SYNTHETIC DETERGENTS are cleansing agents which have all the properties of soaps, but which actually do not contain any soap. These can be used both IN SOFT AND HARD WATER as they give foam even in hard water. Some of the detergents give foam even in ice cold water.
- Synthetic detergents are mainly classified into three categories: ANIONIC DETERGENTS, CATIONIC DETERGENTS AND NON-IONIC DETERGENTS.
- Anionic detergents are sodium salts of sulphonated long chain alcohols or hydrocarbons. ALKYI HYDROGENSULPHATES formed by treating long chain alcohols with concentrated Sulphuric Acid are neutralized with alkali to form anionic detergents. Similarly, Alkyl Benzene Sulphonates are obtained by neutralizing alkyi benzene sulphonic acids with alkali.
- In anionic detergents, the anionic part of the molecule is involved in the cleansing action. Sodium salts of alkylbenzene sulphonates are an important class of Anionic Detergents. They are mostly used for household work. Anionic detergents are also used in TOOTHPASTES.
- CATIONIC DETERGENTS ARE QUARTEMARY AMMONIUM SALTS of amines with acetates, chlorides or bromides as anions. Cationic part possesses a long hydrocarbon chain and a positive charge on nitrogen atom. Hence, these are called CATIONIC DETERGENTS. CETYLTRIMETHYL- AMMONIUM BROMIDE is a popular cationic detergent and is used in hair conditioners. Cationic detergents have germicidal properties and are expensive, therefore, these are of limited use.
- Non-ionic detergents do not contain any ion in their constitution. One such detergent is formed when stearic acid reacts with polyethylene glycol. Liquid dishwashing detergents are non-ionic type. Mechanism of cleansing action of this type of detergents is the same as that of soaps. These also remove grease and oil by micelle formation.
- Main problem that appears in the use of detergents is that if their hydrocarbon chain is highly branched, then bacteria cannot degrade this easily. Slow degradation of detergents leads to their accumulation. EFFLUENTS CONTAINING SUCH DETERGENTS REACH THE RIVERS, PONDS, ETC. These persist in water even after sewage treatment and cause foaming in rivers, ponds and streams and their water gets polluted.
- These days the branching of the hydrocarbon chain is controlled and kept to the minimum. Unbranched chains can be biodegraded more easily and hence pollution is prevented.
- CHLORINE CONTAINING ANTIBIOTIC, CHLORAMPHENICOL, produced by soil microorganisms is very effective for the treatment of typhoid fever. Our body produces iodine containing hormone, thyroxine, the deficiency of which causes a DISEASE CALLED GOITRE. Synthetic halogen compounds, viz. chloroquine is used for the treatment of malaria; halothane is used as an ANAESTHETIC DURING SURGERY. Certain fully fluorinated compounds are being considered as potential blood substitutes in surgery.
- DICHLOROMETHANE is widely used as a solvent as a paint remover, as a propellant in aerosols, and as a process solvent in the manufacture of drugs. It is also used as a metal cleaning and finishing solvent.