Organic Reactions PATHWAYS

Reaction pathways Series of steps to convert one organic compound into a different organic product Putting together a reaction pathway is a lot like doing a puzzle Start with given materials  determine final product Figure out how to use starting materials to create final product You may find it easier to go backwards!

Retrosynthetic analysis Start by looking at the desired product = target molecule Look at what is needed to make that target = precursors Follow a path to what is given in the problem = starting material

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Produce propyl ethanoate from propene and ethene: We know we need an ester. What is used to make the ester? Alcohol and carboxylic acid How do we make a carboxylic acid? Oxidation of a primary alcohol How do we make alcohols from alkenes (propene/ethene)? Hydration RXNs (addition) Which one needs to be made into a carboxylic acid? Ethanol

Produce propyl ethanoate from propene and ethene CH3-CH=CH2 + H2O  CH3-CH2-CH2OH (addition reaction) Propene water propan-1-ol CH2=CH2 + H2O  CH3-CH2OH (addition reaction) Ethene water ethanol CH3-CH2OH + [O]  CH3-CHO + [O]  CH3-COOH (oxidation 1º alcohol) Ethanol (O from K2Cr2O7) ethanal ethanoic acid CH3-CH2-CH2OH + CH3-COOH  CH3-CH2-CH2-O-CO-CH3 (esterification RXN) propan-1-ol ethanoic acid propyl ethanoate

Summary of Alkane reactions (substitution RXNs) Alkanes Convert to halogenoalkanes Halogenoalkanes Convert to dihalogenoalkanes Convert to alcohols

Summary of substitution reactions Alkanes convert to halogenoalkanes or dihalogenoalkanes via a substitution reaction A Hydrogen in alkane replaced with halogen atom from a halogen molecule Uses exposure to UV light Halogenoalkanes convert to alcohols via a nucleophilic substitution reaction Halogen in the halogenoalkane is replaced with an -OH group via an SN1 or SN2 mechanism

Summary of Alkene reactions (Addition RXNs) Alkenes Convert to alcohols Convert to alkanes Convert to halogenoalkanes Convert to dihalogenoalkanes Convert to polyalkene/polymer

Summary of Addition reactions Alkenes convert to alcohols via addition reaction Water added across double bond in presence of an acid catalyst (like sulfuric acid) Alkenes convert to alkanes via addition reaction Hydrogen gas added across double bond in presence of nickel catalyst and heat

Summary of Addition reactions Alkenes convert to halogenoalkanes or dihalogenoalkanes via addition reaction Hydrogen halide or Halogen added across double bond At room temperature Alkenes convert to polyalkene via addition reaction Repeated units of alkene are added to each other by breaking the double bond

Summary of alcohol reactions (oxidation rXNs) 1º alcohols Convert to aldehydes or to carboxylic acids 2º alcohols Convert to ketones Alcohols combined with carboxylic acids To form esters

Summary of alcohol reactions (oxidation rXNs) 1º alcohols convert to aldehydes via oxidation RXN Acidified potassium dichromate (H+/K2Cr2O7) added to alcohol and heated As aldehyde produced, removed via distillation  Aldehydes convert to carboxylic acids via a 2nd oxd. Aldehydes produced via oxidation of 1º alcohols can be “refluxed” with H+/K2Cr2O7 to yield the carboxylic acid 2º alcohols convert to ketones via an oxidation reaction H+/K2Cr2O7 added to alcohol and heated

Summary of alcohol reactions (Esterification RXNs) ~condensation~ Alcohols combined with carboxylic acids to form esters via a condensation reaction Water removed in the presence of conc. H2SO4 -OH from carboxylic acid and –H from alcohol Alcohol becomes prefix of ester name Carboxylic acid becomes stem of ester name

Benzene reactions & Reduction reactions Convert to substituted benzene Nitrobenzene Convert to phenylamine (aniline) Carbonyl compounds Convert to alcohols Reverse of oxidation of alcohols

Benzene reactions (substitution of benzene) Benzene combines with nitronium ion to form nitrobenzene via electrophilic substitution Conc. H2SO4 catalyst, nitric acid, and 50°C Produces nitrobenzene and water Benzene combines with halogens to from halogenobenzene via electrophilic substitution AlCl3 and dry ether (anhydrous conditions) Forms halogenobenzene and H-X

Reduction reactions Nitrobenzene convert to phenylamine via reduction Sn, conc. HCl for first step NaOH for second step All under reflux conditions (in boiling water bath) Carbonyl compounds convert to alcohols via reduction Carboxylic acids/aldehydes convert to primary alcohols LiAlH4 in dry ether with heat Ketones convert to secondary alcohols NaBH4(aq) with heat

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