the synthesis of azo dyes, aspirin and soap

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Michael Ofori

 


Introduction

The reason why I selected these three compounds which are azo dyes, aspirin and soap is because:

  • In the aspect of chemistry, they all have different functional groups and molecular shapes associated with different functions.
  • They are all demanded in the modern world commercially.
  • They are easy and an affordable way of making in the college lab with minor hazards.

The aims of this unit is to:

  • A clear awareness of a variety of different functional groups and their reactions.
  • A brief understanding of the reaction mechanism involved in each reaction as well as the shape importance of the molecule relating to it’s use.
  • An in depth insight of the organic synthesis as well as the gradual steps involved in making the product, including the issue of equilibrium reactions and predicted yield.
  • Familiarize myself

with the different apparatus as well as materials used in the organic synthesis, and their limitations with regardless of yield.

  • Show good comprehensive knowledge of the commercial importance of organic compounds and the economic imperatives involved in producing such compounds.

AZO DYES

1) Introduction

There are different types of dyes. A dye is used to impart color to materials of which it becomes the integral part. They give bright, high intensity colors that can even supply a complete rainbow of colors.

Azo dyes are highly important commercially as they are used in the textile industry as acid dyes for wool and their affinity for cotton is increased by the number of auxochromes or azo groups. Auxochromes are groups in a dye molecule that influences the color due to the chromophore. They are groups, such as –OH and –NH2, containing lone pairs of electrons that can be delocalized along with the delocalized electron

An azo group is a –N=N- group that is a chromophore (A chemical group capable of selective light absorption resulting in the coloration of certain organic compounds.) Azo dyes are also used as pigments and in color photography. In the UK, companies like James Robinsons Limited make about thirty thousand tones of azo dyes each year.

2) Commercial And Laboratory Synthesis

The synthesis of azo dyes involves the reaction of diazotation and coupling and at the end of the reaction, separation of the azo dye from the mixture that is going to be produced.

  1. Diazotisation

This is the reaction in which produces diazonium salt as well as a –N diazonium ion. This is very unstable when it exceeds temperatures above 10°C. Otherwise the –N decomposes into nitrogen gas.

  1. Coupling

This is the electrophilic substitution on the phenol which produces an energetically stable azo dye. The azo group is –N=N-

First step: Diazotisation reaction

                                HNO    + HCL                                                    + 2H O

                             

             Phenylamine   +   nitrous acid + hydrochloric acid     phenyldiazonium chloride + water

                                                                                                            (Diazonium salt)

The reaction takes place under 10°C to prevent the NN, the N2 diazonium ion decomposing into N2 gas. This suggests that the delocalization of the diazonium ion bond electrons over the benzene ring is only able to stabilize the diazonium salt at cold temperatures. At higher temperatures above 10°C, there is too much so therefore the diazonium ion gives way to nitrogen gas.

Below shows the reaction mechanism of for the formation of diazonium salt.

Now that there is a N2+ diazonium ion, there is now a suitable electrophile to attack a phenol ring.

Second Step: Coupling

This is where phenol attacks benzene at the 4th position of the ring. The equation for this

Is:

      Phenyldiazonium ion + phenol              4-hydroxyphenylazobenzene + hydrogen ion

Azo dyes are very stabilized which is a result of broad delocalization of the electrons through the -N=N azo group (nitrogen double bond). Delocalisation is simply increased stability

  1. Relationship Structure/ Function Of Azo dyes

The structure of an azo dye is very closely linked to it’s function as a dye, in terms of color and fastness. Auxochromes can modify the color of a chromophore. The azo functional group itself is also important as this is what part of the light the spectrum absorbs. In the aspect of the fastness, azo dyes are very stable as a result of their chemical structure and they can also be made more color fast by alkylation of phenolic groups

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ASPIRIN

  1. Introduction

Aspirin is one of the commonly used pain relief tablets on the world. It is an analgesic, anti-inflammatory, antipyretic inhibitor of platelet aggregation. Aspirin inhibits the enzyme that converts fatty acids in cell membranes into prostaglandin precursors known as endoperoxides. These endoperoxides can be converted into various prostaglandins, including those that produce pain, fever, and inflammation. Generally, one or two 5-grain doses of aspirin can block the prostaglandin formation.

The main side effect of aspirin is the tendency of irritation of the stomach lining which causes small amounts of blood loss. In ...

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