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Aldehydes, Ketones and Carboxylic Acids

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Aldehydes, Ketones and Carboxylic Acids DGT MH –CET 12th CHEMISTRY Study Material 1 12 Aldehydes, Ketones and Carboxylic Acids SECTION-I: ALDEHYDES AND KETONES (b) CH 3 CH 2 CH(CH 3 )CHO 2-methyl butanal (c) CH CH(CH )CH CHO 3-methyl butanal Section-I: Halogen Derivatives of Alkanes 3 3 2 (d) (CH 3 ) 3 CCHO 2,2-dimethyl INTRODUCTION propanal Aldehydes and ketones are carbonyl compounds, (e) CH CH COCH CH 3-pentanone they contain carbonyl (>C=O) group. General 3 2 2 3 (f) CH COCH CH CH 2-pentanone formula of aldehydes and ketones is C H O. 3 2 2 3 n 2n (g) CH COCH(CH ) 3-methyl Definitions: 3 3 2 2-butanone Aldehydes: These are first oxidative products of primary alcohols, in which carbonyl carbon Metamerism : atom is attached to, at least one H- atom. These Metamerism is present in same class of are presented asR-CHO. compounds. It is shown by the compounds which e.g.H–CHO CH –CHO have different alkyl groups( nature or type) 3 attached to either side of polyvalent functional formaldehyde acetaldehyde group. Ketones: These are first oxidative products of e.g. pentan-2-one and pentan-3-one are secondary alcohols, in which carbonyl carbon metamers, not position isomers. atom is attached to two same or different alkyl CH CH COCH CH diethyl ketone groups. These are represented as, R–CO–R. 3 2 2 3 CH COCH CH CH methyl, n-propyl e.g. CH –CO–CH CH –CO–C H 3 2 2 3 3 3 3 2 5 ketone acetone ethyl methyl ketone pentan-2-one and 3-methyl butan-2-one are ISOMERISM IN ALIPHATIC ALDEHYDES metamers not chain isomers AND KETONES : CH 3 COCH 2 CH 2 CH 3 2 pentanone Aldehydes : They shows chain tautomerism, CH COCH(CH ) 3-methyl, Optical isomerism themselves and functional 3 3 2 2-butanone isomerism with ketones. Note: Metamers are either chain or position Ketones: They shows chain, tautomerism ,optical isomers. If metamerism is mentioned then never isomerism, metamerism themselves and write chain or position isomerism. functional isomerism with aldehydes. Tautomerism: (i) C 3 H 6 O Definition: It is one type of functional isomerism, (a) CH CH CHO propanal 3 2 in which a single compound exists in two or more (b) CH COCH propanone 3 3 readily interconvertible structures that differ in (ii) C 4 H 8 O the relative position hydrogen. (a) CH 3 CH 2 CH 2 CHO butanal Only -H atom involved in tautomerism (b) CH 3 CH(CH 3 )CHO 2-methyl propanal e.g. Acetone and prop-l-en-2-ol are tautomers (c) CH COCH CH 2-butanone 3 2 3 O OH (iii) C H O || | 5 10 CH C CH CH C CH 3 3 2 3 (a) CH 3 CH 2 CH 2 CH 2 CHO pentanal DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448 DGT MH –CET 12th CHEMISTRY Study Material 2 Aldehydes, Ketones and Carboxylic Acids 15 STRUCTURE OF CARBONYL GROUP (b) Vapours of secondary alcohols are 1. Carbonyl group (> C = O) consist of one passed over Cu or Fe metal at 573 K sigma and one bond. undergo dehydrogenation gives ketones. 2. In carbonyl group carbonyl carbon atom is Cu /573 K CHOH C O H 2 in sp 2 hybridised state. Note: Tertiary alcohols are heated 2 3. The sigma bond is formed by sp hybrid with copper metal at 573 K undergoes orbital of carbon and p-orbital of oxygen i.e. dehydration to give alkenes and water. sp 2 -p overlappling. 3. From hydrocarbon 4. The bond is formed by sideways overlapping (a) Ozonolysis of alkene : of unhybridisedp-orbital of carbon and p-orbital of oxygen i.e., p-p overlapping. CH2 CH 2 O 2 CH O CH |2 | 2 5. Carbonyl carbon atom is joined to three atoms O O 0 of sigma bond making a bond angle 120 , ethylene ozonide therefore, carbonyl group has trigonal planer Zn structure. CH2 O CH 22 H O Zn(OH) 22 Zn(OH) 2H CHO 6. In carbonyl group, oxygen is more O O electronegative than carbon hence oxygen ethylene ozonide carries partial negative charge (nucleophilic or (b) Hydration of alkyne Lewis base centre) and carbon carries partial CH CH H O 40 % H2 SO 4 positive charge (electrophilic or Lewis acid 2 10 % HgSO 4 centre). CH CHOH rearrangement CH CHO 7. The high polarity of carbonyl group is 2 3 explained on tbe basis of resonance structure. Vinyl alcohol acetaldehyde ----- 4. From dry distillation (pyrolysis or - CO CO decarboxylation) of calcium salt of acids neutral dipolar structure structure (a) Aldehydes: PREPARATION OF ALDEHYDES AND dry distilled KETONES (H COO)2 Ca H CHO CaCO 3 cal. formate formaldeyde 1. By oxidation of primary and secondary alcohols by using pyridinium chloro (b) Ketones : chromate (PCC) or pyridinium e.g.(C 2 H 5 –COO) 2 Ca+(CH 3 –COO) 2 Ca dichromate (PDC): cal.propionate Cal.acetate It oxidises only primary alcohol to aldehyde dry distilled 2C H –CO–CH + 2CaCO and secondary alcohol to ketones. PCC is 2 5 3 3 the mixture pyridine, CrO and HC1 in 1:1:1 ethyl methyl ketone ratio. This reagent does not attack >C=C< 5. From alkaline hydrolysis of geminal bond. It is also known as Collin's reagent. dihalide: The geminal dihalides are boiled with aqueous KOH or NaOH. It produces e.g. CH OH [O] PCC H CHO HO 3 2 aldehydes and ketones. 2. By dehydrogenaion of primary and secondary alcohols by using Cu or Fe | | C X 2KOH C OH 2KX or Ag metals at 573 K. | | X OH (a) Vapours of primary alcohols are passed gemin al dihalide unstable over Cu or Fe metal at 573 K undergo dehydro-genation gives aldehydes. | These are – elimination reactions. COH COHO 2 | Cu / 573 K OH CH2 CH CHO H 2 CHEMISTRY- MHT-CET DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448 DGT MH –CET 12th CHEMISTRY Study Material 3 Aldehydes, Ketones and Carboxylic Acids 16 PREPARATION OF ONLY ALDEHYDES : O 1. Rosenmund reduction ( Reduction of || CH3 (CH 29 ) C H C 25 H OH acyl chloride): Acid chloride is reduced by undecanoate Lindlar catalyst to give aldehyde. Function 5. From hydrocarbon : of BaSO 4 is to poison the catalyst at aldehyde stage. Aromatic aldehydes and its derivatives are prepared from aromatic hydrocarban by O O following methods. || || Pd BaSO 4 RCClH 2 quinoline RCHHCl Strong oxidising agent oxidies hydrocarbon into acids. It is possible to stop the oxidation e.g. Pd BaSO 4 CH3 COCI H 2 quinoline at aldehyde stage using suitable reagent, that convert methyl group into intermediate which acetyl chloride is difficult to oxidised further. CH COH + HCI 3 (i) Etard reaction (oxidation of toulene acetaldehyde by chromyl chloride (CrO 2 Cl 2 ) 2. Stephen's reduction (Reduction of When toulene is oxidised by CrO 2 Cl 2 first give chrominum complex which cyanide by SnCl 2 + HCl) on acid hydrolysis gives benzaldehyde RCN2[H] SnCl2 HCl RCHNH imin e CH 3 CS H2 O 2 R CHO NH 2CrO2 Cl 2 H 3 SnCl2 HCl e.g. CH3 C N 2[H] H2 O OCrOHCl 2 CHO CH CH NH CH CHO NH 3 H 3 3 CH H O acetaldimine acetaldeyde 2 OCrOHCl 2 3. Reduction of cyanide by di-isobutyl benzaldehyde aluminium hydride (iso-but) Al–H or 2 2CrO Cl 2H E(CH ) CHCH ] Al–H Di-iso-but- 2 2 2 3 2 2 2 (ii) Oxidation of toluene by CrO Al–H 3 (chromium oxide) in acetic anhydride RCN2[H] (iso but)2 Al H RCHNH imin e CH 3 CrO3 / 273 k H2 O 2[O] (CH3 CO) 2 O R CHO NH H2 O H 3 (iso but) Al H CHO 2 OCOCH 3 H O e.g. CH3 C N 2[H] CH 3 OCOCH 3 CH C NH H2 O CH CHO NH 3H 3 3 acetaldimine acetaldeyde benzylidene diacetate 2CH3 COOH 4. Reduction of ester by (Iso-but) Al–H 2 (iii) By side chain chlorination followed O by hydrolysis(commercial method). || (iso but)2 Al H R C OR' 2[H] dry ether CH 3 UVL Cl 2 O || R C H R' OH CHCl 2 e.g. 2KOH hydrolysis O CHO || (iso but) Al H 2 CH3 (CH) 29 C OCH 26 2[H] dry ether 2KCl 2H O ethyl undecanoate 2 CHEMISTRY- MHT-CET DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448 DGT MH –CET 12th CHEMISTRY Study Material 4 Aldehydes, Ketones and Carboxylic Acids 17 (iv) By Gatterman - koch reaction: In CHEMICAL PROPERTIES: this reaction –H in benzene ring is Mechanism in Nucleophilic addition converted into –CHO reactions: anhy. CHO The carbonyl group has two active centre which AlCl / CuCl 2CO HCl 3 HCl can, be easily attacked. The positively changed carbon is easily attacked by nucleophile and negaively charged oxygen is easily attacked by PREPARATION OF ONLY KETONES: electrophile. 1. From acyl chloride and dialkyl cadmium: During addition reaction nucleophile attack first Recently dialkyl cadmium is used for and followed by electrophile, because anion preparation of ketones from acyl halide in produced is more stable than cation. the presence of R–MgX. Since ketone formed in reaction do not react further to During the nucleophilic addition reaction preduce 3 0 alcohol. It may be noted that hybridisation of carbonyl carbon atom changes R–MgX can not be used in place of dialkyl from sp 2 to sp 3 .
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