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Transcript
Organic Chemistry Aldehydes and Ketones Chapter 17 Aldehydes and Ketones Carbonyl Present Group C=O O C H in aldehydes and ketones O R C O H Aldehydes R C R' Ketones Aldehydes Aldehydes Sometimes abbreviated RCHO Contain at least one H connected to the C H2C O formaldehyde O O O C H R CH3 CH acetaldehyde benzaldehyde C H Aldehydes Ketones Ketones Carbonyl C is connected to two alkyl groups RCOR’ O O CH3 C CH3 acetone CH3 R C R' CH3 CH2 C O methyl ethyl ketone Ketones Nomenclature IUPAC – Suffix is “-al” for the aldehydes – Suffix is “-one” for the ketones – # indicates position of ketone O CH3 CH2 CH propanal O CH3 CH2 CH2 C CH2 CH3 3-hexanone Nomenclature NOTE: Ketone, Not keytone From Yahoo Images Nomenclature An Aldehyde or Ketone takes precedence over any previously considered group OH O Cl CH2 CH CH2 CH2 CH 5-chloro-4-hydroxypentanal O H2 C CH CH 2 C CH 2 Cl 1-chloro-4-penten-2-one Nomenclature Common H2C names - aldehydes O formaldehyde O O C H CH 3 CH acetaldehyde benzaldehyde Nomenclature QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Common names - ketones – Some are always used O C O CH3 C CH3 acetone benzophenone - Others name each R group and end with “ketone” CH3 CH3 CH2 C O methyl ethyl ketone CH3 O CH3 C C CH3 CH3 methyl t-butyl ketone Physical Properties Carbonyls: Cannot form H bonding with each other: There is NOT an H connected to a F, N, O Aldehydes and Ketones are POLAR molecules and form dipole interactions Gives higher boiling and melting points C O Physical Properties Aldehydes and Ketones – can form H bonds with water! – solubility in water is about the same as alcohols yes! C O C C O O H O H Physical Properties Strong odors – Ketones generally have pleasant odors » perfumes, flavoring agents – Aldehydes odors vary » some pleasant cinnaminaldehyde, vanillin » some not pleasant formaldehyde Many are found in natural products http://www.youtube.com/watch?v=KDohVakqkic How do you make Aldehydes? Aldehydes from Oxidation of 1o alcohols – Problem is over oxidation to ACID! CH3 CH2 OH + K 2Cr2O7 H+ O CH3 CH acetaldehyde ethanol O CH3 CH acetaldehyde + K 2Cr2O7 H+ O CH3 C OH acetic acid Practice a couple ………….. How do you make Ketones? Ketones from Oxidation of 2o alcohols OH CH3 CH CH3 + K 2 Cr2 O7 H+ 2-propanol O CH3 C CH3 acetone + K 2 Cr2 O7 O CH3 C CH3 acetone H+ Practice a couple ………….. N.R. Oxidation of Aldehydes Aldehydes are easily oxidized – KMnO4 – K2Cr2O7 – even air oxidation O O CH3 CH acetaldehyde carboxylic acid! + KMnO 4 CH3 C OH acetic acid Oxidation of Ketones Ketones resist oxidation: – under mild or normal conditions, no reaction – more severe conditions yield mixtures – CO2 and H2O under extreme conditions O CH3 C CH 3 acetone normal conditions [O] N.R. This difference in reactivity can be used to Tell the difference between an aldehyde and ketone Reaction 1. Oxidation – Tollens Test - Benedicts Test 2. Reduction – Hydrogen addition – NaBH4 reagent 3. Addition of Alcohols – hemiacetal/acetal and tautomerism Tollen’s Test The Silver Mirror Test Oxidation of Aldehydes Ag+ ion in aq. ammonia NO reaction with KETONES Ag(NH3)2+ + aldehyde Ag+ + 2 NH3 Ag(NH3)2+ + RCHO Silver Mirror Ag(NH3)2+ Ago + RCOO- + 4NH3 Benedict’s Test Oxidation of Aldehydes Cu++ ion, aqueous Orange to red ppt. NO reaction with KETONES Cu2+ Cu++ + aldehyde Cu+ Cu+(oxide) + acid Benedict’s Test Oxidation of Aldehydes overall reaction O R C H + 2 Cu 2+ + 5 OH aldehyde O Cu2O + 2 Cu 2O + 3 H 2O R C Ocarboxylic acid (ion) Chemical Properties Addition – – – – to C=O Other reactions are ADDITION Reactions Bond is polar + and Negatives are attracted to C Positives are attracted to O + C O Addition of H2 Reduction to Alcohols – Hydrogen gas and a catalyst (Ni, Pd, Pt) – Similar to alkene to alkane reduction O CH3 CH acetaldehyde H2 catalyst OH CH3 CH2 ethanol Addition of H2 Reduction to Alcohols – Will reduce ketones to 2o alcohols – Slower reaction than reduction of C=C » C=C is reduced faster (first) if both C=O and C=C O CH 3 C CH 3 acetone O CH3 CH CH CH 2-butenal H2 Pt H2 Ni OH CH 3 CH CH 3 2-propanol O CH3 CH2 CH2 CH butanaldehyde Addition of H2 using NaBH4 Reduction to Alcohols – NaBH4 does not allow the reaction of the carbon carbon double bond NaBH4 O OH H2O OH Addition of Alcohol In the addition of R-OH to form an “acetal” the First step is the formation of a “hemiacetal” This is when an -OH and -OR are both on same C O CH3 CH + CH3 CH2 OH acetaldehyde ethanol OCH 2CH3 CH3 C H OH hemiacetal (not isolated) Formation of Acetals IF strong acid (HCl) is present, a second alcohol reacts to form the acetal (two -OR groups on C) OCH 2CH3 CH3 C H OH hemiacetal (not isolated) H+ CH3 CH2 OH OCH 2CH3 CH3 C H OCH 2CH3 acetal + H2O Addition of Alcohol - Acetals O Step 1 OCH 2CH3 CH3 CH + acetaldehyde CH3 CH2 OH ethanol OCH 2CH3 Step 2 CH3 C H OH hemiacetal (not isolated) H+ CH3 CH2 OH CH3 C H OH hemiacetal (not isolated) OCH 2CH3 CH3 C H OCH 2CH3 acetal + H2O Formation of Acetals Addition of R-OH – acid catalyzed, 2 moles of alcohol react O CH3 CH2 CH2 CH butyraldehyde OH CH3 CH CH3 + isopropyl alcohol H+ ? Formation of Acetals Addition of R-OH – acid catalyzed, 2 moles of alcohol react O CH3 CH2 CH2 CH butyraldehyde OH CH3 CH CH3 + isopropyl alcohol Draw the Hemi H+ H3 C CH CH3 O CH3 CH2 CH2 CH O H3 C CH CH3 acetal Formation of Acetals Acetal reaction in equilibrium H3C CH CH3 O CH3 CH2 CH2 CH + 2 H 2O O H3C CH CH3 H+ O CH3 CH2 CH2 CH OH + 2 CH3 CH CH3 Formation of Acetals Acetal reactions CH2CH2 C H + O H+ CH3 CH2 OH ethanol ? Formation of Acetals Acetal reactions CH2 OH + O CH3 CH H+ ? Formation of Acetals Hemiacetal reactions (formation of hemiacetals) – likely when within the same molecule 5 4 3 2 1 CH 2 CH 2 CH 2 CH2 CH OH O or 5 H O O O OH 1 2 4 3 a cyclic hemiacetal Formation of Acetals Cyclic hemiacetals – Reacts with a 2nd. molecule of alcohol – Results in a cyclic acetal O OH H+ O OR' + R'-OH a cyclic hemiacetal a cyclic acetal Formation of Acetals QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Which are hemiacetals / acetals? OCH 3 OH O CH 2 CH 3 CH 3 CH 2 CH 2 C CH 3 O CH 3 1 CH3CH2 O CH2CH2 OH 2 3 O O CH3 4 CH3 CH OH 5 OH OH O CH2 CH3 CH3 CH2 CH2 CH CH CH3 7 CH3CH2 O CH2 OH OH O 8 6 OCH 3 9 CH3 C CH3 O CH3 OCH 3 O H 10 Keto-Enol Tautomerism Equilibrium that exists Keto (carbonyl) to Enol (alkene/alcohol) H H C H C H H O acetaldehyde H C C H O H "enol" form Keto-Enol Tautomerism Equilibrium called Tautomerism H H C H C H H O Keto form acetaldehyde (more stable) H C C H O H "enol" form (less stable) Keto-Enol Tautomerism Equilibrium O called Tautomerism O CH3 C CH2 C CH3 2,4-pentanedione OH QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. O CH3 C CH2 C CH3 "enol" form (more stable) Most enols are less stable Important Compounds Formaldehyde – Gas at RT – Soluble in H2O – Formalin » 37% formaldehyde » found in labs » preserves by denaturing proteins – Used to produce polymers H H C O formaldehyde Important Compounds H H Acetaldehyde – bp 21o C – Converted to trimer H C C O H acetaldehyde » 3 units of acetaldehyde » called paraldehyde » once used as a hypnotic/sleep-producer Important Compounds Acetone – bp 56o C – Infinitely soluble in H2O – Excellent industrial solvent: » paints, varnishes, resins » coatings, nail polish – Produced in the body » diabetic ketoacidosis » “acetone breath” H O H H C C C H H H acetone Important Compounds -chloroacetophenone – lachrymators » tearing of eyes, etc. – Used as a tear gas – Active ingredient in “Mace” Cl H2C C O -chloroacetophenone