Carbonyl Compounds and Nucleophilic Addition

Carbonyl compounds Contain at least one carbonyl group. R = R’ or R  R’

Aldehydes  terminal carbonyl groups propanal butanal pentanal No need to specify the position of the carbonyl group

pentan-2-one pentan-3-one

cyclohexanone cyclohexanecarbaldehyde cyclohexylmethanal cyclohexylethanal

benzaldehyde 1-phenylethanone diphenylmethanone benzophenone

4-oxopentanoic acid 5-oxopentanoic acid 4-oxopentanal

Physical Properties 1. Most simple aliphatic ketones and aldehydes are liquids at room temperature except methanal (b.p. = 21C) and ethanal (b.p. = 20.8C) Aliphatic aldehydes have an unpleasant and pungent smell Ketones and aromatic aldehydes have a pleasant and sweet odour

Aldehydes: Methanal HCHO -21 -92  Ethanal CH3CHO 20.8 -124 0.783 Physical properties of some aldehydes and ketones Name Molecular formula Boiling point (oC) Melting point (oC) Density at 20oC (g cm-3) Aldehydes: Methanal HCHO -21 -92  Ethanal CH3CHO 20.8 -124 0.783 Propanal CH3CH2CHO 48.8 -81 0.807 Butanal CH3(CH2)2CHO 75.7 -99 0.817 Methylpropanal (CH3)2CHCHO 64.2 -65.9 0.790 Benzaldehyde C6H5CHO 179 -26 1.046

2. Less dense than water except aromatic members Name Molecular formula Boiling point (oC) Melting point (oC) Density at 20oC (g cm-3) Ketones: Propanone CH3COCH3 56.2 -95.4 0.791 Butanone CH3COCH2CH3 79.6 -86.9 0.806 Pentan-2-one CH3CO(CH2)2CH3 102 -77.8 0.811 Pentan-3-one CH3CH2COCH2CH3 -39.9 0.814 3-Methylbutan-2-one CH3COCH(CH3)2 95 -92 0.803 Hexan-2-one Phenylethanone CH3CO(CH2)3CH3 C6H5COCH3 127 202 -56.9 19.6 0.812 1.028

Boiling point : - (similar molecular masses) carboxylic acid > alcohol > aldehyde, ketone > CxHy Presence of polar group Absence of –OH group

Solubility Small aldehydes and ketones show appreciable solubilities in water due to the formation of intermolecular hydrogen bonds with water

Solubility Ethanal and propanone are miscible with water in all proportions. Propanone(acetone) is volatile and miscible with water  Once used to clean quick-fit apparatus potentially carcinogenic

Solubility Methanal gas dissolves readily in water Aqueous solutions of methanal (Formalin) are used to preserve biological specimens Methanal(formaldehyde) is highly toxic

Industrial preparation By dehydrogenation (oxidation) of alcohols Further oxidation is prohibited Out-dated

Laboratory preparation Oxidation of alcohols 1 alcohol  aldehyde  carboxylic acid 2 alcohol  ketone Further oxidation of aldehyde to carboxylic acid is prohibited by (i) using a milder O.A., e.g. H+/ Cr2O72

Laboratory preparation Oxidation of alcohols 1 alcohol  aldehyde  carboxylic acid 2 alcohol  ketone Further oxidation of aldehyde to carboxylic acid is prohibited by (i) using a milder O.A., e.g. H+/ Cr2O72 (ii) distilling off the product as it is formed

70C > T > 21C

Heating under reflux Ethanol  ethanoic acid

carboxylic acid 2 alcohol  ketone Further oxidation of ketone to carboxylic acid has not synthetic application since 1. it requires more drastic reaction conditions 2. it results in a mixture of organic products High T

2. Reduction of acid chlorides The catalyst Pd or BaSO4 is poisoned with S to prevent further reduction to alcohol

oxidation reduction Aldehydes  Intermediate oxidation state Carboxylic acid or acyl chloride Aldehyde Alcohol reduction Aldehydes  Intermediate oxidation state  Preparation must be well controlled.

Friedel-Crafts acylation (Preparation of aromatic ketones)

4. Decarboxylation of calcium salts Symmetrical ketones can be obtained by heating a single calcium carboxylate

Cross decarboxylation is preferred 4. Decarboxylation of calcium salts Aldehydes can be obtained by heating a mixture of two calcium carboxylates Cross decarboxylation is preferred

Decarboxylation of sodium salts gives methane or benzene. (p. 30 and p NaOH(s) from soda lime fusion CH3COONa(s) CH4 + Na2CO3 NaOH(s) from soda lime fusion + Na2CO3

Keto-enol tautomerism 5. Catalytic hydration of alkynes enol ketone Keto-enol tautomerism

Keto-enol tautomerism 5. Catalytic hydration of alkynes enol Keto-enol tautomerism aldehyde

6. Ozonolysis of symmetrical alkenes

Unsymmetrical alkenes give a mixture of two carbonyl compounds making subsequent purification more difficult. 1. O3 2. Zn dust / H2O

Reactions of Aldehydes and Ketones Nucleophilic Addition Reactions (AdN) Condensation Reactions (Addition-Elimination) Iodoform Reactions (Oxidation) Oxidation Reactions Reduction Reactions

Bonding in the Carbonyl Group The carbonyl carbon atom is sp2-hybridized sp2 – 2p head-on overlap   bond 2p – 2p side-way overlap   bond The  and  bonds in the C = O bond

The carbonyl group is planar(sp2-hybridized) and highly polarized due to (i) Polarization of  bond (inductive effect) (ii) Polarization of  bond (mesomeric effect) + 

Susceptible to nucleophilic attack +  50%

Bond Enthalpy (kJ/mol) : C=C (611) < 2 C–C (346) ( bond <  bond) C=O (749) > 2 C–O (358) ( bond >  bond) Due to polarization of the C-O  bond

Nucleophilic Addition Reactions (AdN) Acid-catalyzed More susceptible to nucleophilic attack

Nucleophilic Addition Reactions (AdN) Base-catalyzed Stronger nucleophile

AdN vs AdE (Non-polar) + 

Reaction mechanism Slow (r.d.s.) H+ and Nu added across the C=O bond Fast

Q.52 50% H+ 50% A racemic mixture

Reactivity depends on two factors : - (i) Electronic effect (ii) Steric effect

(i) Electronic effect Electron-deficiency of carbonyl C  Ease of nucleophilic attack  Reactivity 

> Decreasing reactivity Decreasing positive charge on carbonyl carbon

Carbonyl C is less positive due to delocalization of positive charge to the benzene ring. Or, The C-O bond has less  character  less mesomeric effect

Reactivity : - >

(ii) Steric effect No. /bulkiness of R groups at carbonyl C  Steric hindrance  Reactivity 

Increasing steric hindrance Decreasing reactivity > Increasing steric hindrance

pentan-3-one

Reactivity of AdN : - Aldehydes > ketones Aliphatic > aromatic

Q.53 Reactivity : -

Examples of AdN 1. Addition of Hydrogen Cyanide

1. Addition of Hydrogen Cyanide

Mechanism : - HCN is very toxic  in situ preparation NaCN + H2SO4  NaHSO4 + HCN

Mechanism : - HCN is a weaker nucleophile than CN NaCN + H2SO4  NaHSO4 + HCN excess

Mechanism : - A mixture of CN/HCN is a buffer of pH  9 NaCN + H2SO4  NaHSO4 + HCN excess pKa of HCN = 9.4

The reaction mixture is buffered at pH 9 to ensure highest yield at greatest rate. If pH < 9, H+ + CN HCN The equilibrium position shifts to the right  [CN]   Reactivity 

The reaction mixture is buffered at pH 9 to ensure highest yield at greatest rate. If pH > 9, [H+]   The equilibrium position shifts to the left  Yield 

Used for lengthening the carbon chain 1. LiAlH4/dry ether 2. H2O Dry ether is used as LiAlH4 reacts violently with water H2O(l) + H(aq)  H2(g) + OH(aq) from AlH4

HCN adds preferentially to C=O leaving C=C and benzene ring unaffected. At pH 9, H+ is not concentrated enough to trigger electrophilic attack

HCN adds preferentially to C=O leaving C=C and benzene ring unaffected. No reaction Or, H in HCN is not positive enough to trigger electrophilic attack

HCN adds preferentially to C=O leaving C=C and benzene ring unaffected. +

Q.57 Cl and HSO4 are much weaker bases and nucleophiles than CN to trigger nucleophilic attacks.

Q.54 CH3CH2CHO  CH3CH2CH2COOH excess NaCN H2SO4 H2 Ni 70% H2SO4 reflux

2. Addition of Sodium Hydrogensulphate(IV) excess & saturated Excess NaHSO3 should be used to shift the equilibrium position to the right (yield )

2. Addition of Sodium Hydrogensulphate(IV) excess & saturated Q.55 Since the equilibrium position lies on the right Acidity : -OH < -SO3H

More stable Less stable

Very sensitive to steric hindrance  limited to aliphatic aldehyde and sterically unhindered ketones

The aldehydes and ketones can be regenerated by treating the bisulphite addition product with H+(aq) or OH(aq) Used for the purification of carbonyl compounds

Q.56 Outline how you can separate a mixture of butanone (b.p. = 79.6°C) and 1-chlorobutane (b.p. = 78.5°C) in ether. The mixture of butanone and 1-chlorobutane cannot be separated by distillation as (1) their boiling points are too close (2) butanone tends to decompose below its b.p. (p.91, 1st paragraph)

Ionic  water soluble

organic layer (with 1-chlorobutane) aqueous layer (with adduct)

CH3COC2H5 + NaCl + H2O + SO2

organic layer (with butanone) aqueous layer (with NaCl)

Diethyl ether has a much lower b.p. (34.6C)  can be removed easily without decomposition of butanone

toxic Not recommended NaHSO3 NaCN SN

Condensation (Addition-Elimination) Reactions H2O + Addition

Overall reaction : - phenylhydrazine HO–NH2 hydroxylamine NH2–NH2 hydrazine 2,4-dinitrophenylhydrazine Brady’s reagent 2,4-DNP

Reaction with hydroxylamine cis or trans oxime

Reaction with hydrazine

Reaction with hydrazine Examples : -

Reaction with phenylhydrazine phenylhydrazone

Reaction with 2,4-dinitrophenylhydrazine coloured ppt

Examples : -

Identification of carbonyl compounds Derivatives (e.g. oximes) of carbonyl compounds are insoluble solids with have sharp m.p. The carbonyl compounds can be identified by preparing their solid derivatives followed by recrystallization and metling point determination (checked against data books)

2. Reaction with 2,4-Dinitrophenylhydrazine Brady’s reagent is especially important in this respect since the products (2,4-dinitrophenylhydrazones) are coloured ppt with sharp melting points.

Melting point of 2,4-dinitrophenyl-hydrazine (oC) M.p. of 2,4-DNP derivatives of some aldehydes and ketones Name Molecular formula Melting point of 2,4-dinitrophenyl-hydrazine (oC) Aldehydes: Methanal HCHO 167 Ethanal CH3CHO 168 Propanal CH3CH2CHO 156 Butanal CH3CH2CH2CHO 123 Benzaldehyde C6H5CHO 237

Melting point of 2,4-dinitrophenyl-hydrazine (oC) M.p. of 2,4-DNP derivatives of some aldehydes and ketones Name Molecular formula Melting point of 2,4-dinitrophenyl-hydrazine (oC) Ketones: Propanone CH3COCH3 128 Butanone CH3CH2COCH3 115 Pentan-2-one CH3CH2CH2COCH3 141 Pentan-3-one CH3CH2COCH2CH3 156 Hexan-2-one CH3CH2CH2CH2COCH3 107 Phenylethanone C6H5COCH3 250

Q.58 (a) For cyclopentanone, 1. Prepare BOTH oxime and 2,4-DNP derivatives. Oxime 2,4-DNP Methyl propyl ketone 58C 144C cyclopentanone 50C 142C 2. Purify the products by recrystallization. 3. Determine the melting points of the derivatives and compare the results with those in the above table.

4-methylcyclohexanone Q.58 (a) For 4-methylcyclohexanone, 1. Prepare BOTH oxime and 2,4-DNP derivatives. Oxime 2,4-DNP propanone 59C 126C 4-methylcyclohexanone 37C 130C 2. Purify the products by recrystallization. 3. Determine the melting points of the derivatives and compare the results with those in the above table.

C. Iodoform Reactions NaOH/I2 + CHI3(s) warm CHI3(iodoform) : - a yellow crystal with a characteristic smell

C. Iodoform Reactions NaOH/I2 + CHI3(s) warm Used as a test for carbonyl compounds with at least one methyl group attached to the carbonyl C.

C. Iodoform Reactions ethanal NaOH/I2 + CHI3(s) warm The only aldehyde that gives +ve result is ethanal

C. Iodoform Reactions NaOH/I2 + CHI3(s) warm Give two ketones that give +ve results

O.A. NaOH/I2 + CHI3(s) warm NaOH/I2 warm

Iodoform test CH3OH -ve 1 alcohol CH3CH(H)OH only 2 alcohol CH3CH(CH3)OH, CH3CH(C2H5)OH, …… 3 alcohol All give –ve results

+ve, turns cloudy immediately Lucas test : ZnCl2/conc.HCl CH3OH -ve 1 alcohol -ve 2 alcohol +ve within 5 mins 3 alcohol +ve, turns cloudy immediately

Reaction with Na CH3OH 1 alcohol 2 alcohol 3 alcohol Colourless gas burns with a pop sound 1 alcohol Colourless gas burns with a pop sound 2 alcohol Colourless gas burns with a pop sound 3 alcohol Colourless gas burns with a pop sound

Reaction with KMnO4/H+ CH3OH +ve, gas bubbles(of CO2) 1 alcohol +ve CH3OH  HCOOH  CO2(g) + H2O CH3OH +ve, gas bubbles(of CO2) 1 alcohol +ve 2 alcohol 3 alcohol -ve

NaOH/I2 + CHI3(s) warm H+ Preparation of carboxylic acid with one less C atom than the starting compound

Solid removed by filtration Q.59 heat KMnO4/OH + Purification is difficult

Only ONE organic product is formed (refer to p.93) Oxidation reactions of ketones have no synthetic use except Only ONE organic product is formed (refer to p.93)

D. Oxidation 1. Oxidized to carboxylic acids by strong O.A. O.A. : - KMnO4/H+ or OH K2Cr2O7/H+ conc. HNO3

D. Oxidation 1. Oxidized to carboxylic acids by strong O.A. Ease of oxidation : - Aldehyde > ketone Aliphatic > aromatic

2. Oxidized to salts of carboxylic acids by mild O.A. O.A. : - Tollen’s reagent Fehling’s reagent Benedict’s solution

Unstable  freshly prepared Reactions with Tollen’s reagent (silver mirror test) Preparation of Tollen’s reagent, [Ag(NH3)2]+ Adding aqueous ammonia solution to silver nitrate solution until the precipitate of silver(I) oxide just redissolves. 2Ag+(aq) + 2OH(aq)  Ag2O(s) + H2O(l) Ag2O(s) + 4NH3(aq) + H2O(l)  2[Ag(NH3)2]+(aq) + 2OH(aq) Unstable  freshly prepared

 RCOONH4+ + 2Ag(s) + H2O + 3NH3 Reactions with Tollen’s reagent (silver mirror test) +1 +3 +1 2[Ag(NH3)2]OH + RCHO  RCOONH4+ + 2Ag(s) + H2O + 3NH3 Forming a silver coating (mirror) on the surface of glassware.

 RCOONH4+ + 2Ag(s) + H2O + 3NH3 Reactions with Tollen’s reagent (silver mirror test) +1 +3 +1 2[Ag(NH3)2]OH + RCHO  RCOONH4+ + 2Ag(s) + H2O + 3NH3 Black solid deposit is formed instead of the silver mirror if the surface of the glassware (e.g. test tube) is not clean.

 RCOONH4+ + 2Ag(s) + H2O + 3NH3 Reactions with Tollen’s reagent (silver mirror test) +1 +3 +1 2[Ag(NH3)2]OH + RCHO  RCOONH4+ + 2Ag(s) + H2O + 3NH3 No reaction with ketones Aliphatic aldehyde > aromatic aldehyde

 RCOONH4+ + 2Ag(s) + H2O + 3NH3 Reactions with Tollen’s reagent (silver mirror test) +1 +3 +1 2[Ag(NH3)2]OH + RCHO  RCOONH4+ + 2Ag(s) + H2O + 3NH3 Forming highly explosive silver nitride when the resulting mixture is heated to dryness 2Ag3N(s)  6Ag(s) + N2(g) + energy

Preparation of Fehling’s reagent Reactions with Fehling’s reagent/Benedict’s solution Preparation of Fehling’s reagent Mixing solution A (CuSO4(aq)) with solution B (tartrate / excess NaOH) Deep blue solution due to complex formation of Cu2+ with tartrate

Preparation of Benedict’s solution Reactions with Fehling’s reagent/Benedict’s solution Preparation of Benedict’s solution Mixing solution A (CuSO4(aq)) with solution B (citrate / excess NaOH) Deep blue solution due to complex formation of Cu2+ with citrate

Forming a reddish brown ppt of Cu2O Reactions with Fehling’s reagent/Benedict’s solution from Cu(II) complex +1 +3 +2 +1 RCHO + 2Cu2+ + NaOH + H2O  RCOONa+ + Cu2O(s) + 4H+ Forming a reddish brown ppt of Cu2O

Only aliphatic aldehydes give +ve results Reactions with Fehling’s reagent/Benedict’s solution +1 +3 +2 +1 RCHO + 2Cu2+ + NaOH + H2O  RCOONa+ + Cu2O(s) + 4H+ Only aliphatic aldehydes give +ve results No reaction with aromatic aldehydes and ketones.

Tollen’s /Fehling’s reagents are used to distinguish between aldehydes and other organic compounds

Reagents commonly used to distinguish between aldehydes and ketones Result Reagent Aldehyde Ketone KMnO4/H+ Give acids with the same number of C atoms readily (Purple to colourless or brwon) More difficult, gives acids of fewer C atoms (Purple to colourless or brown)

Give acids with the same number of C atoms readily (Orange to green) Reagents commonly used to distinguish between aldehydes and ketones Result Reagent Aldehyde Ketone K2Cr2O7/H+ Give acids with the same number of C atoms readily (Orange to green) No observable change

Silver mirror is formed Reagents commonly used to distinguish between aldehydes and ketones Result Reagent Aldehyde Ketone Tollen’s reagent Silver mirror is formed No observable change

Reddish brown ppt is formed with aliphatic aldehydes only Reagents commonly used to distinguish between aldehydes and ketones Result Reagent Aldehyde Ketone Fehling’s reagent Reddish brown ppt is formed with aliphatic aldehydes only No observable change

Reagents commonly used to distinguish between aldehydes and ketones Result Reagent Aldehyde Ketone I2/NaOH (Iodoform test) Yellow ppt is formed for ethanal only Yellow ppt is formed for ketones with -CH3 attached to carbonyl group

No observable except with propanone Reagents commonly used to distinguish between aldehydes and ketones Result Reagent Aldehyde Ketone Schiff’s reagent Pink colour appears No observable except with propanone

Schiff’s reagent Preparation : - Passing SO2 to magenta (a red dye) solution until it becomes colourless

Schiff’s reagent Principle : - SO2 bleaches the dye leaving a colourless solution SO2 + H2O H2SO3 H2SO3 + H2O HSO3 + H3O+ HSO3 + H2O SO32 + H3O+ SO32 + magenta SO42 + colourless solution

SO2 + H2O H2SO3 (1) H2SO3 + H2O HSO3 + H3O+ (2) HSO3 + H2O SO32 + H3O+ (3) SO32 + magenta SO42 + colourless solution (4) Sterically unhindered aldehydes or propanone react with HSO3 to give bisulphite adduct

SO2 + H2O H2SO3 (1) H2SO3 + H2O HSO3 + H3O+ (2) HSO3 + H2O SO32 + H3O+ (3) SO32 + magenta SO42 + colourless solution (4) [HSO3]   Shifting (1) & (2) to the right (3) & (4) to the left  SO32/SO2 is removed  The red colour of magenta is restored

Q.60 Step 1 : Qualitative tests Iodoform test  +ve result Schiff’s reagent  +ve result The liquid is either ethanal or propanone

Q.60 Step 2 : Confirmatory tests Preparation of 2,4-DNP derivatives Purification of products Melting point determination Comparison against values in data book

E. Reduction (to alcohols) 1. Reactions with H2/Ni, Pt or Pd High T & P Ni

2. Reactions with LiAlH4 or NaBH4 Both LiAlH4 and NaBH4 have no reaction with C=C double bond.

2. Reactions with LiAlH4 or NaBH4 NaBH4 is less reactive than LiAlH4  can be used in protic solvent  cannot reduce carboxylic acids and their derivatives to alcohols

Q.61(a) CH3COOH CH3CH2COOH CH3CH2CN PBr3 CH3CH2OH CH3CH2Br heat 1. LiAlH4/dry ether 2. H3O+ reflux H3O+ CH3CH2CN C2H5OH CN PBr3 heat CH3CH2Br

Q.61(b) CH3COOH HCOOH CH3CH2OH 1. LiAlH4/dry ether 1. I2/NaOH 2. H3O+

Q.61(c) conc. H2SO4 heat K2Cr2O7/H+ reflux H3O+(aq)

Q.61(d) H3O+(aq) NH2OH K2Cr2O7/H+ reflux

Explain why there is no such a compound called “ethanone”. 31.2 Nomenclature of Carbonyl Compounds (SB p.4) Let's Think 1 Explain why there is no such a compound called “ethanone”. Answer Ketones are compounds with the carbonyl group situated between two carbon chains or carbon rings. Therefore, the simplest ketone is the one with three carbon atoms. “Ethanone”, however, suggests that there are two carbon atoms in it and it does not exist. Back

31.2 Nomenclature of Carbonyl Compounds (SB p.4) Check Point 31-2 (a) Draw the structural formulae of all carbonyl compounds having the molecular formula C4H8O. Give their IUPAC names. Answer (a)

Check Point 31-2 Answer Back 31.2 Nomenclature of Carbonyl Compounds (SB p.4) Back Check Point 31-2 (b) Draw the structural formulae of all straight-chain carbonyl compounds having the molecular formula C5H10O. Give their IUPAC names. Answer (b)

31.3 Physical Properties of Carbonyl Compounds (SB p.7) Example 31-3 (a) In each pair of compounds below, select the one you would expect to have a higher boiling point. (i) A: CH3CH2CHO B: CH3CH2CH2OH (ii) C: D: (iii) E: CH3CH2CH2CHO F: CH3CH2CH2CH3 (iv) G: H: HOCH2CH2CH2OH (a) (i) B (ii) D (iii) E (iv) H Answer

31.3 Physical Properties of Carbonyl Compounds (SB p.7) Example 31-3 (b) Propanone, CH3COCH3, is completely soluble in water, but octan-4-one, CH3CH2CH2COCH2CH2CH2CH3, is almost insoluble in water. Explain their difference in solubility. Answer (b) The solubility of ketones in water decreases as the hydrophobic hydrocarbon portion lengthens. Back

Is dehydrogenation of alcohols an oxidation or a reduction process? 31.4 Preparation of Carbonyl Compounds (SB p.8) Let's Think 2 Is dehydrogenation of alcohols an oxidation or a reduction process? Answer Dehydrogenation of alcohols is an oxidation process. Back

31.4 Preparation of Carbonyl Compounds (SB p.9) Let's Think 3 What are “primary alcohols” and “secondary alcohols”? Answer Primary alcohols have no or only one alkyl or aryl group directly bonded to the carbon atom bearing the hydroxyl group. Secondary alcohols have two alkyl or aryl groups directly bonded to the carbon atom bearing the hydroxyl group. Back

31.5 Reactions of Carbonyl Compounds (SB p.14) Let's Think 4 Both alkenes and carbonyl compounds are unsaturated compounds. Their principal reactions are addition reactions. What is the major difference between the addition reactions of the two groups of compounds? Answer Alkenes are nucleophiles. They undergo electrophilic addition reactions readily. Carbonyl compounds are electrophiles. They undergo nucleophilic addition reactions readily. Back

Check Point 31-5 (a) Describe briefly how you can distinguish between two carbonyl compounds having similar boiling points. The two compounds can be distinguished by determining the melting points of their 2,4-dinitrophenylhydrazone derivatives.

31.5 Reactions of Carbonyl Compounds (SB p.18) Check Point 31-5 Draw the structural formulae of the major organic products A to C in the following reactions: (i) CH3CH2CHO  A  B (ii) CH3CH2CHO  C KCN / H2SO4 conc. HCl 20 oC 2,4-dinitrophenylhydrazine Answer

Check Point 31-5 Back 31.5 Reactions of Carbonyl Compounds (SB p.18) (i) A: B: (ii) C:

2. Reaction with 2,4-Dinitrophenylhydrazine Purified by recrystallization from ethanol After recrystallization,  the products are filtered under suction  washed with a few drops of ethanol

2. Reaction with 2,4-Dinitrophenylhydrazine The set-up of suction filtration

2. Reaction with 2,4-Dinitrophenylhydrazine Their m.p. can be determined Compare the values with those from data books  identify the original aldehyde or ketone