Saponification

The saponification is, within the general framework, a Chemical reaction transforming a Ester into a carboxylate Ion and a alcohol. It is acted in fact of the Hydrolyze in medium Basique of an ester.

History

Initially this reaction is known to transform the mixture of a Ester (a Fatty-acid) and of a bases strong in a mixture of Savon and Glycérol, from where its name. She was explained in 1823 by the Chimiste French Eugene Chevreul which showed that the greasy Substance are made of a combination between the Glycérol and of the fatty-acids.

Reaction

Properties

Saponification is a slow but total reaction. It is a exothermic Réaction.

There exist several processes of saponification:

  • the batch process or Marseilles old but is always used (detailed article: Household soap).
  • continuous processes.

To accelerate the reaction, one can exploit several factors:

  • to maintain an high temperature;
  • to agitate the mixture welds - ester to make it possible the reagents to more easily meet and to maintain a emulsion.

Mechanism

It breaks up into three stages (more one acidification of the medium if one wants D-to obtain a Carboxylic acid , and either a carboxylate ion).

  • First stage: addition of HO- on ester.

  • Second stage: elimination of the group Alcoholate.

At this stage, the reaction could be finished (what would be very practical, to hydrolize an ester, it would be enough to add soda or potash…). It of it is alas nothing because one forms in this stage, certainly a carboxylic acid, weak acid (pKa lain in general between 3 and 4, but relatively most extremely in the medium, the other being water) but also a very strong base, the ion alcoholate (pKa ranging between 18 and 20). There is thus inevitably reaction acid-bases between the acid most extremely and the strongest base, therefore transformation of the carboxylic acid into carboxylate ion.

  • Third stage: reaction acid-bases between the carboxylic acid and the ion alcoholate.

As one can notice it, this reaction is only mechanism which is irreversible, and (almost) total (1014 < K < 1017). Thus it moves balances of the preceding reactions (by entirely consuming their products), making them also total they (or almost).

Within the framework of the synthesis of a soap, one can stop has this last stage. On the other hand, if one wants to obtain a carboxylic acid, réacidifier is needed the medium:

Applications

Soap synthesis

During this reaction, greasy substances (Grease S or Oil S) are hydrolized in alkaline medium by a base, generally of the Potasse (KOH) or Soude (NaOH), at a temperature ranging between 80 and 100 °C. The high temperature is used to accelerate the reaction of saponification. The Saponification of the produced greasy substance of the Glycerol and a Carboxylate mixture of (of sodium or potassium) which constitutes the soap.

The index of saponification is one of the parameters which make it possible to assess the quality of a vegetable Huile. It is the quantity of Potasse KOH, expressed in milligrams, necessary to the saponification of one gram oil.

See too

Random links:Gerard Onesta | The Bay of the Angels | Bilten | Johan de Witt | .st | Parapuã