Aldehydes & Ketones. Chapter 6. Dr. Seham ALTERARY. Chem 340-2nd semester

Transcription

1 Aldehydes & Ketones hapter 6 Dr. Seham ALTEAY

2 hapter out lines Definition & General Structure Aldehydes. ommon Names for Aldehydes. IUPA Nomenclature of Aldehydes. Definition & General Structure Ketones. ommon and IUPA Naming of Ketones. Physical Properties of Aldehydes and Ketones. Preparation of Aldehydes and Ketones. eactions of Aldehydes and Ketones.

3 What are aldehydes and ketones? Aldehydes and ketones are simple compounds which contain a carbonyl group - a carbon-oxygen double bond. 1) Aldehydes General formula: or = The aldehyde group is always at the end of a chain, so it will always take number 1. In aldehydes, the carbonyl group has a hydrogen atom attached to it together with either - a second hydrogen atom - or, more commonly, a hydrocarbon group which might be an alkyl group or one containing a benzene ring.

4 Aldehyde Acid hapter 6; Aldehydess& Ketoness ommon Names for Aldehydes ommon names for aldehydes are derived from the common names of carboxylic acids. They often reflect the Latin or Greek term for the original source of the acid or the aldehyde. Formic acid Acetic acid Propionic acid Butyric acid Valeric acid Formaldehyde Acetaldehyde Propionaldehyde Butyraldehyde Valeraldehyde

5 Aromatic aldehydes are usually designated as derivatives of the simplest aromatic aldehyde, Benzaldehyde. Examples: Benzaldehyde m-nitrobenzaldehyde (o-hydroxybenzaldehyde) Salicylaldehyde p-methoxybenzaldehyde Anisic aldehyde

6 IUPA Nomenclature of Aldehydes Select the longest carbon chain containing the carbonyl carbon. The -e ending of the parent alkane name is replaced by the suffix -al. The carbonyl carbon is always numbered 1. (It is not necessary to include the number in the name.) The group is assigned the number 1 position and takes precedence over other functional groups that may the present such as, =. If the presence of another functional group demands the use of a suffix, the aldehyde group is named with the prefix formyl-. Name the substituents attached to the chain in the usual way.

7 IUPA Naming ommon: IUPA: Formaldehyde Acetaldehyde Propionaldehyde Butyraldehyde Methanal Ethanal Propanal Butanal Examples Methyl butanal l 2-chloropropanal 3-hydroxypropanal 2-pentenal

8 2) Ketones General formula: ( and =alkyl or aryl) ommon name: listing the alkyl substitutents attached to the carbonyl group, followed by the word ketone. IUPA system: relpace the ending ane by the suffix one. The chain is numbered in such a way as give the lowest number to the = group. If another group has priority, then the ketone group is called "oxo.

9 ommon & IUPA Naming ommon: Dimethylketone Diphenylketone Methylphenylketone acetone Benzophenone acetophenone IUPA: Examples: yclobutanone Propanone diphenylmethanone 1-phenylethanone 3 2 Ethylcyclopentylketone 1-yclopentyl propanone Methyl isopropylketone 3-Methylbutan-2-one

10 Physical Properties of Aldehydes and Ketones A. Boiling Points Because of polarity of carbonyl groups, aldehydes and ketones are polar compounds. Dipole-dipole attractions, although important, are not as strong as intractions due to hydrogen bonding. Dipole-dipole interaction amang carbonyl compounds As a result, the boiling points of aldehydes and ketones are higher than those of nonpolar alkanes, but lower than those of alcohols.

11 B. Solubility in water The lower aldehydes and ketones are soluble in water because they form hydrogen bonds with water. Intermolecular hydrogen bonding between water and aldehydes ' Intermolecular hydrogen bonding between water and ketones. Aldehydes and ketones with less than six carbons are essentialy insoluble in water. The higher aldehydes and ketones are soluble in organic solvents such as; benzene, ether, and carbontetrachlorid.

12 Preparation of Aldehydes and Ketones The major methods for preparing aldehydes an ketones are: 1. xidation of alcohols 2. zonolysis of alkenes. 3.ydration of alkynes 4.Friedel-rafts acylation

13 1. xidation of alcohols The oxidation of primary alcohols, using mild oxidizing agents yields aldehydes. [] represents the oxidizing agent used. 1 alcohol An Aldehyde Mild oxidizing agent 3 2 [] 3 [] = r 3 / pyridine or u/ heat When strong oxidizing agents are used, the aldehydes are very easily oxidized to further carboxylic acids. 1 alcohol 3 2 Strong oxidizing agents [] [] = 2 r A carboxylic acid

14 Secondary alcohols, are converted either into ketones on treatment with both mild or strong oxidizing agent. 2 alcohol 3 3 [] 3 3 [] = may be r 3 / pyridine ; u/ heat or 2 r 2 7 For oxidizing a tertiary alcohol, Nothing happens. A Ketone 3 alcohol 3 3 [] No eaction 3 This reaction also illustrates the importance of differentiating between primary, secondary, and tertiary alcohols.

15 2. zonolysis of alkenes esults in aldehydes or ketones depending on structure of the alkene used. General equation (1) 3 (2) Zn, 2 + Examples 1) 3 2) Zn, 2 + 1) 3 2) Zn, 2 2 2

16 3.ydration of alkynes: Addition of water Water adds to alkynes in the presence of dilute sulfuric acid and murcuric sulfate catalyst. to yield an enol. owever the initially formed enol reacts further to produce a ketone. General equation + 2 gs 4/ 2 S 4 Enol form Keto form Less stable More stable Such isomers, differing only in the placement of a hydrogen atom, are called tautomers.

17 Examples a) gs 4/ 2 S 4 Propyne Acetone b) + 2 gs 4 / 2 S 4 1-yclohexyl acetylene 3 1-yclohexyl ethanadehyde 1-yclohexyl ethananone

18 4- Friedel-rafts acylation A general method for preparing ketones that contain an aromatic ring is the Friedel-rafts acylation reaction. The reaction involves treatment of an aromatic ring with an acylchloride,, in the presence of All 3, which acts as a catalyst. l General equation + l All 3 + l Examples l All l Propionyl chloride Ethyl phenyl ketone Propiophenone

19 eactions of Aldehydes and Ketones Aldehydes and ketones undergo nucleophilic addition reaction to the carbon-oxygen double bond. 1. Addition of metal hydrides: Formation of alcohols. 2. Addition of Grignard eagents : Formation of alcohols. 3-xidations of aldehydes and ketones: a.xidation under acidic conditions/ + b. Under alkaline conditions/ - 4. Tollen s Test: Silver mirror test. 5. Addition of ydrogen cyanide: Formation of cyanohydin. 6- Nucleophilic addition of Acetylide ions: 7- Nucleophilic Addition of Alcohols: Formation of emiacetals and Acetals. 8- Addition of Ammonia and Ammonia Derivatives. 9- Aldol condensation reaction annizzaro reaction.

20 1. Addition of metal hydrides: Formation of alcohols. Metal ydrides; LiAl 4, NaB 4 atalytic hydrogenation reduces aldehydes to produce 1 alcohols & ketones to produce 2 alcohols. (conditions are very similar to those used to reduce alkene double bonds). 2 / Ni Low Pressure Lithium aluminum hydride; LiAl 4 is a very strong reducing agent that will reduce many functional groups in addition to aldehydes and ketones. LiAl 4 Sodium borohydride; NaB 4 is a much weaker reducing agent that basically will reduce only aldehydes and ketones to alcohols. 1)NaB 4 2) 2

21 onclusion Although the same result may be achieved by catalytic hydrogenation, or LiAl 4, but NaB 4 has the advantage of selectively reducing of unsaturated aldehydes and ketones into unsaturated alcohols. Exercise: hoose the best reagent for the following reactions. 2 /Ni or LiAl A] 4 or NaB 4 / 3 Propanal Propanol B] NaB 4 / 3 3-Phenyl-prop-2-en-1-al 3-Phenyl-prop-2-en-1-ol ] 2 /Ni LiAl or 4 yclopent-2-enone yclopentanol

22 2. Addition of Grignard eagents : Formation of alcohols. Grignard reagents are strong nucleophiles that they can serve as nucleophilic addition to carbonyl group. Treatment of an aldehyde or ketone with Grignard reagent followed by water forms an alcohol with new - bond. General equation 1. In case of formaldehyde: Grignard reagents react with formaldehyde to produce primary alcohols. Example: MgBr + 1) Dry Ether 2) MgBr + Formaldehyde 1) Dry ether 2) Alcohol Ethanol

23 General equation 2. In case of other aldehyde: MgBr + ' 1) Dry Ether 2) 3 + ' Grignard reagents react with aldehyde to produce secondary alcohols. Examples: 3 2 MgBr + 3 Aldehyde Acetaldehyde 1) Dry ether 2) Alcohol 2-Butanol

24 General equation MgBr + 3. In case of Ketones: 1) Dry Ether ' '' 2) 3 + '' ' Grignard reagents react with ketones to produce tertiary alcohols. Examples: 3 MgBr + 1) Dry ether 2) ketones 3 Alcohol cyclohexanone cyclohexyl methyl alcohol

25 3-xidations of aldehydes and ketones Aldehydes can be oxidized to carboxylic acid with both mild and strong oxidizing agents. Typical oxidizing agents for aldehydes include either potassium permanganate (KMn 4 ) or potassium dichromate (K 2 r 2 7 ) in acid solution. Benzaldehyde a.xidation under acidic conditions/ + KMn 4 / + Benzoic acid Peroxy acids, such as peroxybenzoic acid ( ) are used to oxidize ketones to esters cyclohexylmethylketone 3 l 3 cyclohexylacetate xygen insertion occurs between carbonyl carbon and larger group.

26 The iodoform test The iodoform test is a test for the existence an acetyl group, or a group that can be oxidized to an acetyl group which will give a positive iodoform test. The General equation b. Under alkaline conditions/ - The compounds containing 3 or 3, give iodoform test. These type of methylketones can be distinguished from other non-methyl ketone by their reaction with iodine; I 2 in a basic solution; Na to yield iodoform (I 3 ) as a yellow colored precipitate. 3 +3I 2 + 4Na I Na NaI -ve Iodoform +ve Iodoform(I 3 ) result = is a pale yellow substance.

27 Examples: a) 3 acetaldehyde Na + 3I 2 I 3 + Na b) 3 acetophenone + 3I 2 Na I 3 + Na c) 3 acetone Na 3 + 3I 2 I Na

28 Exercise: Which of the following compounds will give a positive result +ve toward iodofrom test: ompounds esults Why?? ve, No yellow ppt +ve, gives yellow ppt +ve, gives yellow ppt as no 3 as 3 as 3 -ve, No yellow ppt as no 3

29 eaction Mechanism of haloform verall reaction 3 excess X 2 Na Na + X 3 This reaction happen when you have terminal ketone. aloform could be chloroform, bromoform and Iodoform. Note that α-hydrogens are more acidic due to the inductive effect near by the halogen. As there are excess of halogen; the halogen will replace all the methyl hydrogens.

30 eaction Mechanism of haloform hapter 6; Aldehydess& Ketoness eaction Mechanism Na Br Br Na Na Br Br Br Br Br Br Br Br Br Br Br Br Br Br Br Br + Br Br Br Na Br + Br Br

31 Mechanism Description from sodium hydroxide will attract the hydrogen add create the enolate intermediat. The enolate collapse back dawn and the 1 st halogen adds to the molecule. The reaction happens twice till the three halogens are added. The presence of 3 halogen atoms on the carbon δ+ makes it δ + and difficult to act as leaving group. Br Br Br In the presence of more molecules of Na in the solution the will attack the δ+ forming tetrahydral unstable intermediat. The ve oxygen will collapse back dawn to reform the double bond and kick out the :Br 3 instead of. The :Br 3 anion abstracts a proton from either the solvent or the carboxylic acid formed in the previous step, and forms the haloform and carboxylate ion.

32 4. Tollen s Test: Silver mirror test. Tollen s reagent (Ag(N 3 ) 2 + / - is a weak oxidant Aldehydes are readily oxidized to carboxylic acids by Tollen s reagent to produce a silver mirror on the inside of a clean test tube. Ketones are not oxidized by Tollen s reagent. video link General Equation + 2 Ag(N 3 ) 2 2 Ag + N4 Metalic silver is deposted in a thin mirror coating Ammonium salt of carboxylic acid N 3 Example Ag 2 + Ag N 3 / 2

33 Experiment bservation onclusion Tollen s test The colourless solution produces a grey precipitate of silver, or a silver mirror on the test tube. Aldehyde Tollen s test No change in the colourless solution Ketone

34 5. Addition of ydrogen cyanide: Formation of cyanohydin. The nucleophilic addition of hydrogen cyanide (N) to aldehydes or ketones affords yanohydrin. General equation or ' N, - N or ' N aldehydes or ketones yanohydrin (yanohydrin: A molecule containing an - group and a -N group bonded to the same carbon.

35 Examples: a) N, - N Benzaldehyde N Benzaldehyde cyanohydrin N b) N, - N yclohexanone yclohexanone cyanohydrin

36 yanohydrins are very useful because the N group can be converted to other functional groups. For example: reduction with LiAl 4 followed by water reduces the N group to a primary amine. Thus an aminoalcohol product is formed. 1) LiAl 4 2) 2 2 N 2 2-Amino-1phenyl-ethanol N 3 + heat 2-hydroxy-2-phenylacetic acid Also, hydrolysis of the N group with acidic water gives a hydroxy carboxylic acid product. This affords us with an important method of synthesizing α-hydroxy-carboxylic acids.

37 6- Nucleophilic addition of Acetylide ions: Acetylide ions are another example of organometallic reagents; it can be thought of as organo sodium reagents. They are good nucleophiles. Acetylide ions can also used to attack carbonyl group, The net effect of the reaction of organometallic reagents with an aldehyde or ketone is the addition of the components and across the = double bond. General equation An alkynol The addition of acetylides ions to aldehydes and ketones yields an alkynol. (An alkynol: is an alcohol on carbon adjacent to triple bond.)

38 Examples: a) 3 Na + Formaldehye An alkynol, 1 alcohol b) 3 3 Na + Acetaldehye An alkynol, 2 alcohol c) 3 Na yclohexanone An alkynol, 3 alcohol

39 7- Nucleophilic Addition of Alcohols: Formation of emiacetals and Acetals A.1 emiactals The addition of one mole of an alcohol to the carbonyl group of an aldehyde yields a hemiacetal. (hemi, Greek, half). General equation An Aldehyde + ' + An alcohol ' A hemiacetal B.1 Acetals When hemiacetals are treated with an addition mole of an alcohol in the presence of anhydous acid, they are converted to acetals. General equation " ' + " + (anhyd.) ' A hemiacetal An alcohol Acetals

40 Example 3 Ethanal Methanol 1-Methoxyethanol (A hemiacetal) A.2 emiketals The addition of one mole of an alcohol to the carbonyl group of a ketone yields a hemiketal. General equation + " 3 + (anhyd.) ,1-Dimethoxyethanol (An acetal) + ' + " ' A Ketone An alcohol A hemiketal

41 B.2 Ketals The reaction of hemiketal with alcohols to form ketals is seldom works. '" ' + (anhyd.) + '" ' " " a hemiketal An alcohol ketals The onclusion The hemiacetal and the hemi ketal are compounds that have an alkoxy group () & hydroxy group () that are attached to the same carbone. The acetals & the ketals are compounds that have two alkoxy groups () on the same carbon.

42 8- Addition of Ammonia and Ammonia Derivatives Nitrogen nucleophiles such as ammonia and its derivatives 2 N - Z add to carbonyl group of aldehydes and ketones. The reaction is reversible and catalyszed by acid. The net result is replacement of the > = group with > = N - Z group a) The eaction with ydroxylamine Aldehydes and ketones react with hydroxylamine to form oximes. ' () Aldehyde or Ketone + 2 N ydroxylamine + N + 2 ' () xime

43 b) The eaction with ydrazine Aldehydes and ketones react with hydrazine to form hydrazones. With aldehydes NN 2 NN Acetaldehyde ydrazine Acetaldehyde hydrazone With ketones NN NN Acetone ydrazine Actone hydrazone

44 c) The eaction with ammonia N 3 Like ammonia derivatives ammonia also reacts with aldehydes (except formaldehyde) and ketones to form the products called imines N 2 3 N N 2 Acetaldehyde Ammonia Acetaldehyde ammonia Acetaldimine

45 Summary Structure and names of nitrogen nucleophiles that react with carbonyl compounds: Nitrogen Nucleophile Nitrogen derivative of carbonyl compounds Ammonia N 3 N Imine + ydrazine N 2 N 2 N N 2 ydrazone ydroxylamine N 2 N xime

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47 9- Aldol condensation + Dilute Alkali + Dil. Ba() 2 Aldol means aldehyde and alcohol groups on the same molecule. May occur between two aldehydes (aldols) or two ketones (ketols) in the presence of catalytic base. eaction NLY possible between two components having α-hydrogen. The reactions are reversible - With Aldehydes, the equilbrium favors product - With ketones, the equilbrium favors the sarting materials.

48 Aldol condensation eaction Mechanism Step 1. Ionization of base Na Na + Step 2. Formation of acceptor electrophile Na + Na Step 3. The base removes an acidic alpha hydrogen from one aldehyde molecule; yielding a resonance stabilized enolate ion (nucleophile). + Step 4. The enolate ion attacks a second aldehyde molecule in nucleophilic addtion reaction to give a tetrahydral alkoxide ion intermediate. Na + Na Na Step 5. Protonation of the alkoxide ion intermediate yields neutral aldol product and regenerate the base catalyst. 2

49 Note that: The aldol products formed often undergoes dehydration to form conjugated systems. This reaction is a type of nucleophilic addition In some cases, the adducts obtained from the Aldol Addition can easily be converted (in situ) to α,β-unsaturated carbonyl compounds, either thermally or under acidic or basic catalysis

50 Ketol condensation eaction Mechanism Step 1. Ionization of base Na Na Step 2. Formation of acceptor electrophile + Na + Step 3. Formation of donar enolate nucleophile + Na Step 4. The enolate ion attacks a second ketone molecule giving a tetrahydral alkoxide ion intermediate. + Na Na 2 Na Step 5. Protonation of the alkoxide ion intermediate yields neutral ketol product and regenerate the base catalyst.

51 In similar manner dehydrates takes place in ketols to the α,β -unsaturated compound. Note That: The aldol product cannot be isolated. Dehydration is favorable because the product is stabilized by conjugation of the alkene with the carbonyl group.

52 10- annizzaro eaction Upon treatment with strong bases (e.g. in aqueous Na) and heating, non-enolizable aldehydes undergo redox disproportionation to give corresponding alcohols and carboxylic acids in 1:1 ratio. General equation Examples 2 2

53 eaction Mechanism of annizzaro eaction

54 ome Work Q.1 Each of the following compounds was prepared by an aldol condensation followed by dehydration. In each case, select the structure of the starting material from the list of choices in the box below.

55 Q.2. Give the IUPA name for the following. A) B) Br Q.3 Arrange these compounds in order of increasing Boiling point. Acetone Propan-1-ol Propanal n-butane Methoxyethane (i) (ii) (iii) (iv) (v)

56 Thank you For your attention