Hair Dyes Lecture 7 PDF

Chemistry of dyes (chem 334 L7) By ▪ Dr. Mohamed Ramadan (Ph.D. organic Chemistry , Faculty of Science, MU) Dr. Mohamed R. Elmorsy ❖ Hair dyes Today, hair dyes are widely used, either to cover up grey hairs, or simply by those wanting to...

Chemistry of dyes (chem 334 L7) By ▪ Dr. Mohamed Ramadan (Ph.D. organic Chemistry , Faculty of Science, MU) Dr. Mohamed R. Elmorsy ❖ Hair dyes Today, hair dyes are widely used, either to cover up grey hairs, or simply by those wanting to change their natural hair colour. The chemistry behind how they change the colour of hair can actually get pretty complicated, but this section tries to boil it down to the key classes of chemicals involved, and an overview of the process that produces the dye molecules. )1 Hair structure: Dr. Mohamed R. Elmorsy ▪ The hair shaft is comprised of three layers: the cuticle, cortex, and medulla. ▪ The cuticle is the hair's outer most layer which has shingle or scale like cells that overlap. These cells work defensively to prevent damage to the hair's inner structure and to control water content of hair fiber. ▪ The middle structure includes a thick layer of cells called cortex, its were you find the keratin and the pigment melanin protein that gives hair its color. ▪ These are pigments responsible for the colour of our hair called melanins, of which there are two types: eumelanin, and pheomelanin. Eumelanin causes shades ranging from brown to black, whilst pheomelanin gives colours in the range of blond to red. Darker hair, therefore, contains more eumelanin; generally, eumelanin is often the more abundant of the two types, though red hair contains primarily pheomelanin. Differing hair colours are merely the consequence of different balances in concentrations of these two pigments, and blond hair is often a result of a low concentration of melanin in general. ▪ The innermost structure is the medulla, this layer which is only present in large thick hairs. Dr. Mohamed R. Elmorsy 2) Classification of hair dyes: ▪ Temporary dyes, just stick to the cuticle. It will usually circle the drain with your next shampoo. (Really paint) Dr. Mohamed R. Elmorsy ▪ Semi-Permanent dyes, contain smaller size dyes compared to the temporary, that they can partially penetrate the cuticle and stick to the cortex. It does not chemically react with any thing in the hair , It is still more paint like lasts about 12 shampoos max. ▪ These dyes are mainly based on dyestuffs of nitro-amino dyes ▪ The most important nitro dyes are picramic acid (2-amino-4,6-dinitrophenol,) and 4-Nitro-o-phenylenediamine picramic acid 4-Nitro-o-phenylenediamine Dr. Mohamed R. Elmorsy ▪ Permanent dyes, as the name suggests, is designed to stay with hair until the hair grows of falls out. Its also called oxidative dyes. Permanent dyes Oxidizing Dye Alkaline Couplers agent precursor chemicals Dr. Mohamed R. Elmorsy ▪ Dye precursor: (colorless compounds): they are aromatic compounds generally with functional groups in the para-position ( p-diamines or p- aminophenols). ▪ Developers (oxidizing agent): Hydrogen peroxide Commonly used. Hydrogen peroxide is a strong oxidizing agent and can oxidize the dye precursor to primary intermediate molecules (a reactive species which can react with the coupler and form the dye molecules). Dr. Mohamed R. Elmorsy ▪ Couplers: they are derivatives of benzene which show-NH2 and –OH substitution at meta-position. ▪ Dye parcourses can be also used as a coupler. Dr. Mohamed R. Elmorsy ▪ Alkaline chemicals: The reactions which produce the dyes (coupling between primary intermediate and coupler) are carried out at an alkaline pH (ammonia) to produce the colored dye. m Dr. Mohamed R. Elmorsy Dr. Mohamed R. Elmorsy ▪ Dyeing process in the hair Dye precursor Developer + Coupler + Base Dr. Mohamed R. Elmorsy Base Side effects of permanent dyes ▪ Most types of permanent hair dyes have chemicals, That is why some researchers mention that permanent dyes are the most harmful and harmful types of hair dyes ▪ Most chemicals especially p-phenylenediamine(PPD) and resorcinol are carcinogenic substances. ▪ Most dyes using (ammonia). The ammonia causes the cuticles of the hair to swell, which then allows the dye molecules ( primary intermediates and couplers ) to pass into the hair. So, it usually softness and relax the cuticle scales. The result overtime is dry, brittle, unhealthy looking hair, for this reason, many companies have produced ammonia-free hair dyes, using substitutes such as ethanolamine. This is a milder agent, but also doesn’t cause the cuticle to swell as much as ammonia, meaning it has a few aesthetic drawbacks: it often washes out after a certain time period, unlike permanent colourings which merely grow out, and isn’t as effective at lightening hair. (Ammonia is one of the worst offenders found in the beauty business) ▪ Hydrogen peroxide is a strong oxidizing agent, and can oxidize the natural melanin pigments in hair, removing some of the conjugated double bonds that lead to their color, and making their molecules colourless. More commonly, of course, we refer to this as bleaching the hair. Dr. Mohamed R. Elmorsy Dr. Mohamed R. Elmorsy ‫‪Dr. Mohamed R. Elmorsy‬‬ ‫اللهم اغفر البي وامي واسكنهما الفردوس االعلي من الجنة‬