3.5 Alcohols

Compounds W, X and Y are all carbohydrates with X and Y each containing five carbons.

Compound W and a byproduct, compound Z, are formed from the reaction between compound X and Y.

Compound X can be oxidised by the reaction with acidified potassium dichromate to give compound Y.

2.754 g of compound Y contains 0.027 moles.

Using the information given, state the name of compound Y and justify your answer.

Draw the skeletal formula of compound W and explain how compound Z is formed in the reaction.

Compound X will oxidise to compound Y if allowed to fully oxidise. Explain how a student could stop the full oxidation of compound X.

State the formula of an isomer of compound X that will not react with acidified potassium dichromate, H⁺ / K₂Cr₂O₇.

Using your knowledge of bonds present in the oxidation products of different classes of alcohols, suggest why the isomer you have drawn will not react with acidified potassium dichromate, H⁺ / K₂Cr₂O₇.

Propan-2-ol has a relatively high boiling point. Draw how two molecules of propan-2-ol interact with one another and explain how the strongest type of intermolecular force arises.

Propan-2-ol can undergo oxidation to form a compound which has the formula C₃H₆O.

Propan-2-ol can be dehydrated to propene using concentrated sulfuric acid, H₂SO₄, at a temperature of 170C.

Name and outline the mechanism of the dehydration of propan-2-ol showing the sulfuric acid molecule is involved in the reaction.

The structure of sulfuric acid is shown below in Figure 1.

Figure 1

A student states that the product of dehydration of propan-2-ol will exhibit geometric isomerism. Is the student correct? Justify your answer.

Menthol can be made synthetically or extracted from various kinds of mint plants. It can be used to treat mild aches and pains by causing the skin to feel cool then warm.

The structure of menthol is shown in Figure 1.

Figure 1

State the empirical formula of menthol.

The final step in the synthetic production of menthol is to form the alcohol group from the ketone group in the molecule.

State the formula of the ketone containing compound that will form menthol.

The structure of ascorbic acid is shown in Figure 2.

Grignard reagents as shown above the arrow in Figure 3 are powerful reagents for organic synthesis. The formula for a Grignard reagent can be simplified to R-Mg-X. They can react with esters to produce alcohols.

Figure 3

Ethanol has many uses such as industrial solvent and a raw material to produce a variety of compounds. It can be manufactured on a large scale by two different processes.

Give equations reagents and conditions for both of these processes.

Compare the two methods outlined in part (a) to manufacture ethanol. In your answer make reference to the atom economy, raw materials and the energy required.

The first production car that ran on biofuel was manufactured in Brazil in the 1970s.

Explain which method of production of the ethanol outlined in part (a) can be identified as carbon neutral.

In your answer explain what is meant by the term carbon neutral and give the extent to which your chosen process can be classed as carbon neutral.

Ethanol is converted to ethene only under harsh conditions, concentrated sulphuric acid at 450K. In contrast, 2-methylbutan-2-ol is dehydrated on treatment with acid at 298K. In this reaction, two products are formed.

Ethanol is one of the most important alcohols and has a wide range of uses. Some of its uses include as an intermediate in the synthesis of other organic chemicals, as a solvent, in the manufacture of drugs, and in alcoholic beverages and ink.

Ethanol can be made industrially by fermentation of sugars.

The fermentation reaction described in part (b) only occurs at a temperature between 30 and 42 C.

State two other conditions which are essential for this reaction to occur.

The ethanol produced by fermentation cannot be used straight away as a biofuel as it first needs to be separated by fractional distillation.

Ethanol can be produced from crude oil by cracking and hydration, or from sugars by fermentation. Though the use of biofuels has many advantages, there are also environmental and ethical issues linked to the use of biofuels.

A chemist has access to alcohol A (CH₃)₃CCH(OH)CH₃, acidified potassium dichromate (VI) and concentrated sulfuric acid.

The chemist then reacts alcohol A from part (a) with hot, concentrated sulfuric acid to form product C. She then measures the boiling point of product C and compares it to the boiling point of alcohol A.

The chemist wants to conduct some further research into the reactions of the alcohols, and decides to use isomers of alcohol A.

The chemist also has propan-1-ol which she wants to oxidise to propanal using potassium dichromate (VI). The oxidation of this alcohol may however also produce a second product D depending on the reaction conditions used.

The boiling points of propan-1-ol, propanal and product D are summarised in Table 1.

Table 1

A student wants to convert an alcohol P (CH₃)₃CCH(OH)CH₂OH to a compound which contains an aldehyde functional group only. The student has access to all other chemical reagents.

A mixture of alkenes is produced when butan-2-ol is reacted with hot concentrated sulfuric acid. One of the isomers formed is but-1-ene.

Name and outline the mechanism for this reaction that forms but-1-ene.

The reaction described in part (b) forms a pair of stereoisomers.

State how these stereoisomers arise.

The dehydration of an alcohol produces an alkene. The addition polymerisation reaction of this alkene results in the formation of a polymer is shown in Figure 1.

Figure 1

Draw the structural formula and name the alcohol from which the polymer in Figure 1 is formed.

Many internal combustion engines will run on ethanol or mixtures of petrol and ethanol. Ethanol can be made from ethene which is obtained from crude oil or by fermentation.

Give an advantage of producing ethanol by fermentation over the hydration of ethene which is obtained from crude oil.

Despite the many disadvantages of producing ethanol by fermentation, this method is often promoted as it is claimed that the ethanol obtained in this way is a carbon-neutral biofuel.

One of the disadvantages of this process is that the ethanol produced is impure.

Local farmers are against the decision of the company to produce ethanol by fermentation as they claim carbon is not a carbon-neutral biofuel.

State and explain any arguments that the farmers may have to support their statement.