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Organic Chemistry Lesson 6 Alcohols Refresh Which products can be potentially obtained from crude oil and are economically important? I. II. III. A. B. C. D. Plastics Margarine Motor fuel I and II only I and III only II and III only I, II and III We Are Here Lesson 6: Alcohols Objectives: Explain the relative ease of combustion of the alcohols Describe the oxidation reactions of the alcohols Investigate the oxidation reactions of the alcohols Alcohols General formula is CnH2n+1OH The –OH (hydroxyl) functional group is polar Alcohols are more soluble in water than alkanes of comparable molar mass Alcohols as Fuels Alcohols combust more readily than equivalent alkanes but release less energy since they are already partially oxidised Alcohol + oxygen carbon dioxide + water Alcohols are used as fuels: As a fuel for cars – either pure or blended with petrol Methanol as fuel for competitive motorsports including dragsters and monster trucks Adding a small amount of gasoline improves the engine starting in cold weather Since the 1960s methanol has been the required fuel for the Indianapolis 500 and other types of racing. The reason for this is that methanol is made of a single chemical. Gasoline, on the other hand, contains many different chemicals, and can vary greatly from one batch to another. Methanol is safer in case of accidental fire than gasoline, because it burns cooler. Ethanol used as fuel is fermented from crops (corn, sugar cane)…crops that could otherwise be eaten, forcing up food prices. Is this okay? Oxidation of alcohols The most important reactions of the alcohols are their oxidations A range of compounds will oxidise them so the oxidiser is often represented as [O] One common laboratory oxidising agent you need to know is acidified potassium dichromate, K2Cr2O7. When using this, orange Cr (VI) is reduced to green Cr (III) Oxidation reaction scheme Oxidation of alcohols summary 1⁰ 2⁰ 3⁰ Reduction We can reverse these oxidations using a suitable reducing agent e.g. sodium borohydride in aqueous or alcoholic solution (mild) OR lithium aluminium hydride in dry ether followed by aqueous acid (sledgehammer) e.g. Esterification reaction Alcohols react with carboxylic acids to form esters in a condensation reaction in which water is also produced. This is an equilibrium reaction that must be catalysed by concentrated sulfuric acid. Alcohol + carboxylic acid ester + water Oxidising alcohols Complete the following investigation into the oxidation of alcohols Instructions here Key Points Alcohols are highly combustible Primary alcohols oxidise to form aldehydes, which oxidise to form carboxylic acids Secondary alcohols oxidise to form ketones Tertiary alcohols do not oxidise due to the 3 strong C-C bonds surrounding the –OH carbon These oxidations can be reversed by reduction. Esters can be made by reacting alcohols with carboxylic acids in condensation reactions (water is also produced).