CAIE A-Level Chemistry 15.1.4 Elimination to Form Alkenes

Practise eliminating HX from a halogenoalkane using hot ethanolic hydroxide and drawing the possible alkene products.

Exam points

choose NaOH or KOH in ethanol with heat or reflux to favour elimination rather than substitution
remove H from a carbon adjacent to C–X and remove X to create the new C=C bond
balance the equation to include the alkene, water and sodium or potassium halide products

[Maximum number: 2]

Fig. 4.1 shows a possible synthesis of propene, $\mathrm{C}_{3} \mathrm{H}_{6}$ .

Fig. 4.1

Reaction 3 is an elimination reaction.

Write an equation for this reaction and identify the solvent and conditions used. equation solvent and conditions

(a)(ii)

$\text { M1 } \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{Cl}+\mathrm{NaOH} \rightarrow \mathrm{C}_{3} \mathrm{H}_{6}+\mathrm{H}_{2} \mathrm{O}+\mathrm{NaCl}$

M2 ethanol (solvent) AND heat / reflux

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15.1.4—Elimination reaction with NaOH in ethanol question 1