Carbo Acids & Its Derivatives Flashcards
Factors affecting acidity of carboxylic acids.
- The electron withdrawing grp attached to the OH bond weakens it by withdrawing electrons,enhancing the loss of H (as a proton), hence enhances acidity.
- The negative charge on the carboxylate ion is spread all over the ion, thus stabilizing it & making the combin. with H less likely.
- The group attached to the carboxylic acid group ( if it is e withdrawing, easier for H to be lost. If e pushing, it neutralizes the electron pull of the carbonyl).
About Methanoic acid.
- It is the strongest unsubstituted carbo.acid.
- It is oxidised by mild ox.agents to form CO₂ + H₂O
- Gives positive test with Fehling sol.(Cu² reduced to Cu¹, orange deposits seen) & Tollens reagent (Ag¹ reduced to Ag , silver mirror seen).
- It will change color of both KMnO₄ & K₂Cr₂O₇.
Reaction of Ethanedioic acid .
The Mn(2 plus) ion produced serves as a catalyst. Therefore this is an example of auto catalysis.
Preparing Acyl Chlorides. E.g=> PCl₅
- R.t.p/ no heating
- products-> Acyl chloride, POCl₃, HCl.
- Reagents-> carbo.acid and PCl₅
Preparing Acyl Chlorides E.g => PCl₃
- Requires heating, No catalyst.
- Products-> Acyl chloride & H₃PO₃.
- same reagent as all other preparations.
Preparing Acyl chlorides. E.g => SOCl₂
- R.t.p
- Products -> SO₂ & HCl
- Same reagents as other preparations.
How does converting carbo.acids to acyl chlorides increase its reactivity?
The O of the carbonyl group, as well as the Cl atom will draw electrons strongly from the C atom, making it electron deficient . Hence the carbonyl carbon has a partial positive charge and increased likelihood of neuclophilic attack.
Equation for the general reaction of Acyl chlorides.
ROCL + HZ —–> ROZ + HCl.
HZ -> e.g are: H₂O , ROH, NH₃, RNH₂ cuz of the lone pair of electrons on the oxygen and nitrogen.
R is the alkyl or aryl.
HZ is group acting as neuclophile.
Why are reactions of acyl chlorides faster than that of chloroalkanes?
Cuz of the presence of the carbonyl group making it more open to neuclophilic attack.
Why don’t aryl chlorides undergo hydrolysis?
Cuz the carbon carrying the halogen is part of the delocalised pi bonding system of the benzene ring. Causing the C-Cl bond to have some double bond character.
Reaction of alcohol and phenol with acyl chlorides to produce esters and HCl , this reaction is much faster than the reaction of alcohol or phenol with carbo.acids.
Because of the carbonyl group making it more open to neuclophilic attack.
Why can amines (RNH₂) act as Lewis bases?
Cuz they have a lone pair of electrons on the nitrogen. The nitrogen donates it’s lone pair of electrons to a proton to form a dative bond.
When reacting HCl with ammonia or an amine …. How will the product look?
Add one H to the ammonia or amine making it a + ion and a Cl ion right beside it being a - ion.
The strength of a base is based on ?
The ease or difficulty of loosing the lone pair of electrons on the nitrogen.
Making amines:
Halo.alkane + excess ethanolic ammonia.
- Conditions-> Heat
- Reagents-> Halo.alkanes & excess eth. amm.
- Reason for excess-> prevents formation of secondary & tertiary amines and formation of amm. salts.
Making Amines:
Halo.alkanes + cyanide ion.
- Conditions : Heat , reflux.
- Reagents: Halo.alkane one carbon short of goal & KCN in ethanol.
- The reaction forms a nitrile that can be further oxidised to form an amine.
- Reducing agents: LiAlH₄,NaBH₄, Nickel , H gas.
- Amides can also form amines using LiAlH to reduce it.
Making phenyl amine.
- Made by reducing Nitrobenzene.
- Reagent : Tin in HCl & Nitrobenzene.
- steam distillation is used to get it from the mixture.
Phenyl amine reacts with aq bromine in a similar way to phenol and?
aq bromine.
Diazotisation process. ( formation of azodyes)
- Phenylamine reacts with HNO₂ to produce diazonium salt.
- HNO₂ is unstable so it is made in situ by reacting sodium nitrate with dilute HCl.
- Conditions: reactn. mix must be kept below 10⁰C using ice as the diazonium salt is unstable & decomposes easily giving N gas.
- The ion reacts with an alk. sol. of phenol (coupling).
- The reactn. prod. vry stable azodye (it is orange) cuz the delocalised pi bonding system between 2 benzene rings is extended through the N=N group which acts as a bridge.
- The azo is formed immediately.
Amino acids have 2 func.groups, namely…..
Carbo. acids & Amines.
How is a Zwitterion ion formed ?
By reaction between the -COOH & -NH₂ of the same amino acid. ( the latter gains one H and the former loses its H).
Consequences of the Zwitterion ion.
- Amino acids have relatively strong intermolecular forces of attraction (due to ionic nature) hence they’re crystalline solids and are soluble in water.
- Solution of amino acids act as a buffer (resists PH changes).
How is an Amide formed?
From the reaction between a carbo.acid functional group and amine functional group.
(It means amino acids can form Amide linkages and peptide linkages).
Difference between amides and amines. (In terms of PH).
Amines are basic, while amides are neutral.
