Aldehydes , Ketones And Carboxylic Acids

Welcome to Organic Chemistry Class. In this post we discuss the organic chemistry chapter Aldehydes, Kitones and Carboxylic Acids.

Aldehyde & Ketone are also known as Carbonyl Compound because present of (>C=O) Carbonyl group.

What Is An Aldehyde ?

 An Aldehyde is the first oxidation product of primary alcohol. The functional group is formyl or aldehyde group  (-CHO )always present at the terminal carbon of the chain. 

What Is Ketone ?

A Kitone is the first oxidation product of secondary alcohol. The functional group is keto or oxo group ( >C=O ) not located at the terminal carbon of the chain.

What Is Carbonyl Group ? 

  Carbonyl Group is a functional group in which a carbon atom is attached to an Oxygen atom by a double bond and remaining two valencies of carbon atom are free is called a carbonyl group and represent as >C=O

 

Nomenclature of Aldehydes: Common Name System: (1) The names of aldehydes are derived from the common names of acids. (2) THe suffix ' -ic acid ' of an acid replace by 'aldehyde'. (3) The positions of the substituents in the molecule are indicated by Greek letters α,β,y, etc. starting from the carbon atom attached to the carbonyl group  IUPAC System: (1) The longest carbon atoms chain containing aldehyde carbon atom is selected as a parent                          hydrocarbon. (2) 'e' of the alkane is replaced by 'al'. (3) the position of aldehyde group need not be mentioned since it is a;ways at the end position. (4) The substituent in the alkyl group are prefixed in an alphabetical order by appropriate locants.  Compound         Common name       IUPAC name      HCHO  Formaldehyde   Methanal   CH3CHO  Acetaldehyde   Ethanal

Nomenclature of Ketones:  Common Name System: (1) Ketones are name according to the alkyl groups attached to the carbonyl carbon atom followed by the word ketone (2) The substituents in the alkyl groups are indicated by Greek lettters  α,β,y, etc. starting from the carbon atom attached to the carbonyl group. IUPAC System: (1) The longest continuous chain containing carbonyl carbon atom is selected as a parent hydrocarbon. (2) 'e' of the alkane is replaced by 'one'. (3) The position of carbonyl group is represented by the lowest locant. (4) The substituents in the alkyl groups are prefixed in the alphabetical order along with their positions by appropriate locants.  Compound         Common name       IUPAC name      H3C. COCH3  dimethyl ketone  (acetone)   Propanone  H3C. COC2H5  ethyl methyl ketone    butanone

Preparation Methods Of Aldehyde And Ketone

Aldehyde and Ketone can be prepared by following methods:

1. Oxidation of alcohol 
2. Catalytic dehydrogenation of alcohols
3. Oxidation of alkenes
4. Hydration of alkenes 
5. Hydrolysis of geminal dihalide
6. Pyrolysis of calcium salt of carboxylic acid
7. Reduction of acid chloride
8. Oxo process 
9. Wacker process   

1. Oxidation of alcohol :

            Aldehyde and ketone can be prepared by controlled oxidation of 1° & 2°  alcohol using acidified solution of potassium permanganate KMnO₄ or potassium dichromate K2Cr2O7 . 1° alcohol produce Aldehyde and 2° alcohol produce Ketone.

                                                        

    2. Catalytic dehydrogenation of alcohols :

              When Aldehyde and Ketone can be prepared, when vapor of 1° and 2° alcohol is pass over copper catalyst at 300°C result in the formation of aldehyde and ketone.

                                                               

     3. Oxidation of alkenes  : ( ozonolysis ) 

               When alkene subjected for oxidation with ozone gas and on hydrolysis with zinc dust it gives aldehyde and ketone.

                                                                

      4. Hydration of alkenes :

               when alkene such as Acetylene on hydrogen yield.  water molecule is added to acetylene in the presence of mercuric sulphate HgSO4 and sulfuric acid, it result in the formation of unstable molecule called as enol. which is on entra molecule rearrangement gives acetaldehyde. 

                                                                  

         Hydrogen of alkene other then acetylene gives Ketone. water is added according to marconi rule to form unstable enol, which is on rearrangement gives Ketone.

 

        5. hydrolysis of geminal dihalide :

                   Geminal dihalide are compound which has two halogen attached to same carbon. Ketone, Aldehyde can be prepare by alkene hydrolysis of geminal dihalide in which two halogen atom can be replace with OH group. result in the formation of unstable diol. which is hydration result in the formation of wither Aldehyde or Ketone. 

       6. Pyrolysis of calcium salt of carboxylic acid : 

                 Symmetrical ketone can be prepare by this method, when calcium salt of carboxylic acid is heated at 400°C. we only can prepare ketone by this method and can not prepare aldehyde.

        7. Reduction of acid chloride :

             Aldehyde can be prepare by hydrogenation of acid chloride in presence of platinum supported over barium sulfate solution   

        

• What is Schiff's reagent ?

      Schiff's reagent is an oxidizing agent. Schiff's reagent is prepared by dissolving pink p-rosaniline hydrochloride in water and passing SO2 gas till the pink solution is decolourised.

      When an Aldehyde is added to Schiff's reagent, the colourless solution turns pink or in magenta colour and aldehyde is oxidised to a carboxylic acid. 

Did u know 🤔🤔

•  Formaldehyde is gas at room temperature.
• Formaldehyde is used as a disinfectant. 
• Formaldehyde is use for silvering mirrors. 
• Formaldehyde is use in the preparation of variety of plastics and resins. 
•  Acetaldehyde boils at 20 °C
•  Acetaldehyde is used as a starting material for the preparation of many compounds.
• Acetone is used as a commercial solvent.
•  Acetone is used in manufacture of explosives, lacquers, paint removers, plastic, drugs, perfumes,etc.
• density of aldehyde & ketone is less than water.