Acid Halides.pptx

Acid Halides

1. Acid Halides Submitted to : Dr. M Aslam Submitted by : M.Aneeq Javed

2. Content: Introduction NOmenclature Methods of Preparation Physical properties Chemical Properties

3. Introduction Acid halides are the derivatives of acids in which the OH of carboxyl group has been replaced by a halogen atom The acid halides are also referred to as acyl halides ; the acyl group is R-CO-. The acid chlorides are by far the most important of all the acid halides and will be discussed in detail. Their type formula may be represented as,

4. Nomenclature They are named by dropping the ending - i c acid from either the common name or the IUPAC name and adding the suffix - yl chloride or halide.

5. Methods Of Preparation Acid chlorides are prepared from appropriate carboxylic acids: 1) By reaction with thionyl chloride ( SOCI2): Thionyl Chloride reacts with carboxylic acids to produce an acyl chloride, giving off sulfur dioxide and hydrogen chloride gases. For example : This method is superior to others as the by-products being gases escape leaving the acid chloride in the pure state.

6. Cont … 2) By reaction with phosphorus tri-chloride (PCI3 ) When a carboxylic acid reacts with phosphorus tri-chloride ,a mixture of the acyl chloride and phosphorus acid is obtained. For example :

7. 3) By reaction with phosphorus pentachloride (PCI5 ) This reaction leaves a liquid mixture of acyl chloride and a phosphorus compound, phosphorus tri-chloride oxide (phosphorus oxychloride, POCl 3 ).  For example : It is possible to prepare acid bromides and iodides by reactions analogous to those used in the preparation of chlorides, However, in comparison to the chlorides, they are seldom used.

8. PHYSICAL PROPERTIES (1)All simple acid chlorides are colorless liquids of lower boiling point than the correspondingacid (2) They have sharp pungent smell, and are lachrymators (tear-producing). (3) They emit pale fumes of hydrogen chloride when exposed in air on account of their reactionwith water vapor. (4) They are insoluble in water but slowly dissolve in it because of hydrolysis. (5) The C=O stretching band in IR Spectrum occurs at frequency range 1780-1850 cm¹.

9. Chemical Properties In acyl chloride (RCOCI), we have a carbonyl group attached to a highly electronegative chlorine atom. Due to the electron-withdrawing effect of the Cl atom, the electron density on the carbonyl carbon is diminished further. As a result, acid chlorides are readily attacked by nucleophiles, whereby the Cl atom is replaced by a nucleophile.

10. Cont …. Thus, acid chlorides are very reactive compounds, their characteristic reactions being nucleophilic substitution reactions are as: They react with weak nucleophiles as water, alcohols, ammonia and amines to produce the corresponding acid, ester, amide or substituted amides

11. Cont … Some of their important reactions are listed below : Hydrolysis : Acid chlorides react with water to form carboxylic acids.

12. Cont … Reaction with Alcohol . They react with an alcohol when the chlorine atom is displaced by alkoxy group.-OR', to produce an ester:

13. Cont … Reaction with Ammonia: Acyl chloride reacts violently with a cold concentrated solution of ammonia. A white solid product is formed which is a mixture of ethanamide (an amide) and ammonium chloride .

14. Cont.. Reaction with 1 ° and 2 ° Amines . Acid halides react with 1 ° and 2° amines to produce substituted amides.

15. Cont … Reaction with Salts of Carboxylic Acids Acid chlorides react with carboxylic acids to form  anhydrides.

16. Cont … Friedel -Crafts Reaction: Acylation  is the term given to substituting an acyl group such as CH 3 CO- onto another molecule. An acyl group is a hydrocarbon group attached to a carbon-oxygen double bond. The most common example of an acyl group is the  ethanoyl  group, CH 3 CO-, and this group is used throughout this article. If benzene is reacted with  ethanoyl  chloride in the presence of an  aluminium  chloride catalyst, the equation for the reaction is as follows: