Cosmetics and perfumes (chemistry part-2)

6.SUNTAN LOTION:-

•      Sunlight possesses both beneficial and harmful effects on the skin .
• Exposure to moderate sunlight increases blood circulation, produces vitamin D in the body,kills germs and causes thickening of the skin to prevent sunburn.these are the main beneficial effects.
• However,long exposure may damage the skin producing erythema( reddening),painful burn,blister,swelling of the skin and something skin cancer .
• Some natural protection against sunburn is obtained by thickening of the skin due to increased rate of cell formation  at the epidermis and also increased melanin content of the epidermis.
• The purpose of suntan lotion is to minimise the harmful effects of the sunlight and to assist tanning of the skin .
• The suntan lotions are chemicals which act as sunscreen to absorb at least 85 % of uv- radiation within the wavelength range of 290 nm to  320 nm but allows the passage of longer uv- radiation (>320 nm).this will produce light tanning of the skin.
• A sunscreen lotion should be non-toxic,non-irritating,non-odorous,non-volatilinon-volatile and stable under normal conditions.
• If the sunscreen absorb more than 95 % of uv-radiation to prevent sunburn ,are called true sunscreen agents.

     
    The following groups of chemicals may act as a sunscreens:-

1. p-aminobenzoic acid and its derivatives.
2.  Cinnamic acid derivatives.
3. Salicylates.
4. Anthranilates
5. Lawsone with dehydroxy acetone etc.

A typical formulation of suntan lotion is given as an example:-
Suntan lotion composition
Ingredients.                                                       Percentage (wt)

• ISO butyl para-aminobenzoate                   1.9%
• Hexadecyl  alcohol                                        4.7 %
• Isopropyl alcohol                                           52.6%
• Water                                                                40.3 %
• Carbopol 934                                                   0.5%
• Di-isopropanol amine                                    Small amount.

        The sunscreen, vehicle and other materials should be compatible. In sunscreen formulation sometimes zinc oxide, Calamine are used.
7.HAIR DYES :-

         The major use of the hair dyes in our country is to change the grey colour into black . However, other types of coloration like golden, reddish,greenish, brownish etc. Can also be seen as fashion To a lesser extent.

The hair dyes can be classified into three categories according to their performance, Viz . Temporary, semi permanent and permanent types.
7.1. TEMPORARY HAIR DYES:-

• These belongs to different classes of chemical compounds like Azo, anthraquinone, benzoquinoneimine etc. Giving various sheds of colour from violet to red and black.
• These dyes can be applied as aqueous or alcoholic solution. To increase The attachment of the dye to the hair sometimes  treatment  of the hair with special chemicals is  needed.
• Temporary colouring can also be done by coloured stick, made from crayons and is applied by rubbing on Wet hair.

7.2. SEMI- PERMANENT DYES:-

•  These mostly belong to the following classes of chemical compounds, viz. Nitrophenylenediamines, nitroaminophenol and aminoanthraquinones.
• Dyes developed from these basic compounds produce a large number of different shades of colour which are difficult To obtain by any other method.

This maybe understood by considering the compound 4-nitro-o-phenylenediamine as an example.

4-nitro-o-phenylenediamine

With substituents.

4-nitro-o-phenylenediamine.

Shifting the positions of No2 and NH2 group in the benzene ring as well as changing the type of substitutent will give variation in the depth of colour obtained.

 7.3. PERMANENT HAIR DYES:-.                    

                These are based on oxidation dyes (para-dyes) which are colourless at the time of application on hair but are converted into a coloured material as a result of subsequent reactions occuring on the hair itself.

       In order to develop colour Three Types of chemicals are necessary to react amongst themselves.

        These are:--
a. Bases:-

• these are Benzene derivatives with substitutions in the para or Ortho positions to each other by NH2 and /or OH groups. In these positions easy oxidation occurs to the substituted groups.
• Some of the important compounds of this group are p-phenylenediamine,p-toluenediqmine,p-aminophenol,p-aminophenol etc.

b.couplers:-

•  These are also benzene derivatives having substitution in the meta position to each other by NH2 and /or OH groups. In this position oxidation does not take place easily.
• The most common coupling agents are m-phenylenediamine,m-aminophenol,resorcinol etc.

c. Oxidising agent:-

•  The universally used oxidising agent is hydrogen peroxide. However, as solid oxidising agent urea peroxide or melamine peroxide may be used.
• The oxidation and coupling reactions are carried out in presence of ammonia (alkaline PH) by hydrogen peroxide. The reactions are highly complex as it involves large number of bases and couplers in one formulation.
•  Colour develops gradually but the compounds formed is difficult To specify. Sodium sulphite and ammonium thioglycollate are used as anti-oxidant to prevent premature oxidation of the dye before use.
•  In addition to oxidation, hydrogen peroxide has a bleaching action on hair To produce eveness in dying.
• Hair dyes are available in the form of solution, emulsion, shampoo, gel and powder.
• Black hair dye consist of p-phenylenediamine,p-aminophenol, resorcinol, pyrogallol and 4,4-diaminoanisole sulphate.
• After 40-50 minutes of the application, the excess dye should be washed out thoroughly with water and shampoo.
• Sometimes the p-amino compounds causes irritation and skin allergy as these are toxic chemicals.

8. HENNA:-                                                         

•  Henna is a vegetable hair dye made from the powdered dried leaves of lawsonia alba, lawsonia spinosa and lawsonia inemis.
• The leaves are collected from the plant before flowering which contents 2-hydroxy-1,4-naphthaquinone as the dyeing chemical.
• It is soluble in weak acidic solution and also in hot water.
• For dyeing purpose, powdered Henna is made into a paste with hot water to which Citric or adipic acid is added to make it slightly acidic (PH 5.5).

The acidic paste is applied on hair and kept in position by a towel for about an hour . The hair is then washed and shampooed.

• Heena produces reddish Brown Shades, which is relatively stable. Is may stain finger nails if proper precautions are not taken during application. The Great advantage of Henna is its non-toxic character.

 9.GERANIOL:-                                              

•  It is an alicyclic terpene alcohol obtained as a colourless liquid having sweet rose type odour. its chemical formula    is C10H18O and structurally represented as 3, 7-dimethyl-trans-2, 6-octadiene-1-ol.

Geraniol.

• It is widely distributed in nature. It may be obtained either in the  or as an ester.
• It is present in the volatile oils of rose, geranium , champaca, ginger-grass, citronella and palmarosa.
• Palmarosa oil contains upto 85% Geraniol and citronella oil contains about 20% Geraniol.
• Geraniol with fine fragnance can be produced by the fractional distillation of palmarosa oil.its geraniol content is very high.

However ,fractional distillation of citronella oil yields a fraction containing upto 60% Geraniol.

• Geraniol is used in combination with phenyl ethyl alcohol to give Rose-like fragnance.

    10. CITRONELLA OIL:-

•   This oil is produced from several aromatic grasses available at Ceylon, Java, India, Indonesia, China and America.
• Two varieties of citronella oil is available according to the source. For the Ceylonese variety,the raw materials are fresh or partly dried leaves and stems of a variety of aromatic grass (cymbopogon) which is different from the Java variety of grass.
• Fresh and partly dried stems and leaves are subjected to steam distillation when oil collects as distillate.
• It is a pale yellow liquid with sweet, flowery rose- like odour with strong citrous note.
• It is extensively used as perfume and also acts as a raw material for the preparation of citronellal (a perfume).
• Ceylonese oil processes a grassy camphor-like odour and is used a perfume for toilet soaps and washing powders.

Citronella oil.

11. CIVETONE:-

• Civet is a grandular secretion of both male and female civet cat used by the animal to protect itself.
• The secretion is collected by curetting The civet glands with a spoon. The yellowish greasy substance is stored in aluminium containers.
• The odour is obnoxious in the raw state, but becomes pleasant and attractive on large dilution.
• Civet is extracted with alcohol to make a concentrated solution. It is added in small amounts To floral perfumes To give a sweet character.

The odour giving constituents is a Ketone called civetone. It occurs as a white crystalline substance.

• Civetone is used in fine perfumery for the preparation of high class scent.