OSU CHEM 2520 - Chemical Tests for Aldehydes

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Chemical Tests for Aldehydes!-Fehling's Test!!!!!-Tallen's Test!!!!!!Chapter 19 & 20: Carboxylic Acids and Derivatives Acidity and Basicity!-Resonance stabilized by conjugate base!!!!!!-Increased acidity with presence of EWG (e- withdrawing group) !!!!!!!!Formic Acid Synthesis!!!!Acetic Acid Synthesis via Ethene Oxidation !!!!!Acetic Acid Synthesis via Carbonylation !!!!Synthesis of COOHs!-Oxidation of primary alcohols and aldehydes !-CrO3/KMnO4 (see above)!-dilute HNO3!!!!!-Addition of organometallics to CO2(s)!!!!!!!!!!-Hydrolysis of Nitriles (H+ or B-)!!!!!!!!Substitution at the Carbonyl!-via addition-elimination mechanism !!!!!!!-Base-catalyzed add-elim mechanism !!!!!-H+ catalyzed mechanism !!!!!!!!!!!Carboxylic Acid Derivatives Acyl Halides!-forming acyl halides!!!!!!-mechanism !!!!!!!!!!!!!!!!!!!!!!!!!!Anhydrides!-COOH + acyl halide !!!!!!!!!!!!!!!!!!!!!!!!!!!!Esters!-h+-catalyzed addition to COOH (Fischer esterification) !!!!!-mechanism !!!!!!!!!!!!!!!Amides!-COOH + amine + heat!!!!!-mechanism (H+ catalyzed pathway is difficult)!!!!!!!!!!Carboxylic Acid Chart!-the conversion of one carboxylic acid derivative to another can be summarized in the chart below. You can travel down the chart converting one derivative into another directly, however, you cannot travel up the chart directly. To travel up you must first convert the derivative into carboxylic acid, then you may convert it into the desired derivative. !!!!!!!!!!!!!!!!!Other Reactions of COOHs!-Reduction with LAH!!!!!!-mechanism!!!!!!!!!!-Hell-Vollard-Zelinsky Reaction (HVZ) !-bromonation alpha to acid !!!!!!!-proceeds through an acyl halide/enol precursor !!!!!!!!!!!!!Basicity of COOH Derivatives !-more resonance means more stability and more Basicity !!!!!!!Acidity of Alpha Hydrogens !!!!!!!!pKa Value to Know!!!!!!!!!!!!Alkanenitriles!-Hydrolysis !!!!!!!!!-acid catalyzed mechanism!!!!!!!-base catalyzed mechanism !!!!!!!!-reaction with alkyl nucleophiles !!!!!!!!-Reduction !!!!!!Chapter 18: Enols and Enolates Acidity at the Alpha C !-alpha hydrogens are acidic due to resonance stabilization !!!!!!-Aldehydes are more acidic than ketones !!!!!!!!!!!Formation of Enolates !-weak/moderate bases only partially promote enolate formation !!!!!!!-stronger bases completely promote enolate formation !!!!!!!-also works with KH/NaH and t-BuLi!-Enolates are ambident - can attack from C and O !!Keto-Enol Equilibria!-Tautomerization - rapid equilibrium between keto and enol forms !-keto form is thermodynamically favorable !!!!!!!-base catalyzed enol formation !!!!!-acid catalyzed !!!!!!Halogenation (alpha)!!!!!!!!!!-monohalogenation occurs under acidic conditions!-base mediated process produces polyhaolgenated products!!Alkylation of Aldehydes and Ketones !-base-mediated alkylation is difficult to control!-aldehydes alkylate faster than ketones, but suffer from side reactions !-unsymmetrical ketones!-more stable enolates occur at higher T (thermodynamic control)!-less stable enolates occur at lower T (kinetic control) !-Fastest formed and least substituted side !!!!!!!!-monoalkylations with enamines (enamines are nucleophiles)!!!!!!!!!Aldol Addition !!!!!Aldol Condensation!-protonated by heat!!!!!Direct Dehydration !!!!!!Intramolecular Aldol Reactions!-5 and 6 membered rings favored !!!!!!!!!!!Enones!-enones are more stable than the saturated species because of resonance !!!!!-nonconjugated enones will "walk" into conjugation !!!!!!!-undergo typical reactions of alkenes and carbonyls !-nucleophilic addition to an enone !!!!!!!-weak nucleophiles and organocuprates add 1,4!-thermodynamic control, makes most stable species!-amines, alcohols, CN, enolates, alkoxides...!!!!!!!!!!!! !!-strong nucleophiles add 1,2 !-kinetic control, usually forms unstable products !-organolithiums (RMgX add both)!!!!!-hydrides add 1,2 with aldehydes !!!!!The Michael Addition !-enolate addition to enones, forms 1,5-dicarbonyls compounds!!!!!!!!!!!!The Robinson Annulation (ring forming) !-Michael addition + aldol condensation (intramolecular)!!!!!!!!!!!!Chapter 23: Claisen Condensations Claisen Condensations !-ester enolate + NAS !!!!!!!!!!!!!!!-Retro Claisen (reverse)!!!!!!-mixed Claisen (only one/zero enolizable Hs) !!!!!!!-Intramolecular Claisens (Dieckmann)!!!!!!!Retrosynthesis Analysis!-Aldols give beta-keto alcohols !!!!-Michael Additions give 1,5-dicarbonyls!!!!-Claisens give beta-keto esters (1,3-dicarbonyls) !!!!!!Beta-Dicarbonyl Anions are Nucleophiles!!!!!!!Decarboxylation!!!!!!!!!!-mechanism!!!!!!Acetoacetic Ester Synthesis !-synthesis of substituted ketones!!!!!!Malonic Ester Synthesis!-synthesis of substituted COOHs!!!!!!!Michael Additions!!!!!!Acyl Anion Equivalents!-acyl anions cannot be made!!!!!-Dithianes (cyclic thioacetals)!!!!!!!!!!!-Thioazolium Salts (aldehyde coupling) !!!!!-mechanism!!!!!!!!!!! Chapter 21: Amines !Nucleophilicity and Basicity!-amines are good nucleophiles and bases!-the lone pair on N can act as a nucleophile by attacking the electrophile or it can act as a base by grabbing a proton!-more steric hinderance leads to greater basicity (except tertiary) !!!!!!-aryl amines are less nucleophilic and less basic than alkyl amines because the lone pair is delocalized around the aromatic ring!!Alkylation of Amines !-direct alkylation (through SN2) leads to polyalkylations because the product is still nucleophilic and reactive towards the electrophile!!!!-indirect alkylation is required for monoalkylations!-Cyanide Displacement Reduction !!!!!!-Azide Displacement Reduction !!!!!-Gabriel Synthesis !!!!!!!-mechanism !!!!!!!!!!!!!!-works best with primary alkyl halides as it relies on SN2. Secondary alkyl halides will work but not as well as primary. Will not work with tertiary alkyl halides and aryl halides!!!Reductive Amination !-forming an amine from an imine via reduction !!!!!!Preparation of Amines from Carboxylic Acids!-reduction with LAH!!!!!-Hoffman Rearrangement !!!!-involves the loss of one carbon atom!-useful because it gives us a way to make an amine from any carboxylic acid derivative !!!!!Acylation of Amines !-converting an amine into an amide !!!!!Hoffman Elimination !!!!!-gives least stable alkene because it goes through an anti-zaitsev TS!!!Mannich Reaction!-enol + Imminium !!!!!!!-mechanism!!!!!!!!!!!!Nitrosation!-amines react with nitrosyl cation (NO+)!-nitrosyl cation formation !!!!!!-secondary amines lead to N-nitrosamines

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