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The specified transformation is (CH₃)₃COH + HCl → (CH₃)₃CCl + H₂O: 2-methylpropan-2-ol becomes 2-chloro-2-methylpropane. This is substitution of the alcohol group, not simple dichromate oxidation. Protonation turns the poor hydroxide leaving group into water; in this tertiary case, ionisation can produce a relatively stabilised carbocation which chloride then attacks.
Video by Royal Society of Chemistry. This RSC demonstration follows the specified alcohol–hydrochloric acid preparation, including separation, washing, drying and distillation. Explain the reason for each stage before trying the questions.
Viewing focus: Explain conversion of the tertiary alcohol to a chloroalkane
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: How is the OH group made a better leaving group in this reaction?
It is protonated so water can leave. Acid changes the leaving group before substitution.
After watching 2: What is removed by a hydrogencarbonate wash?
Residual acid. Acid–hydrogencarbonate reaction produces CO₂ and needs controlled venting.
What you'll be able to do
The specified transformation is (CH₃)₃COH + HCl → (CH₃)₃CCl + H₂O: 2-methylpropan-2-ol becomes 2-chloro-2-methylpropane. This is substitution of the alcohol group, not simple dichromate oxidation. Protonation turns the poor hydroxide leaving group into water; in this tertiary case, ionisation can produce a relatively stabilised carbocation which chloride then attacks.
The laboratory’s method uses concentrated hydrochloric acid under controlled conditions. Corrosive acid and volatile flammable organic materials require the approved ventilation, protection, quantities and handling. A reagent’s availability is not a reason to change the method or heat a closed mixture. The mechanism explains why a tertiary alcohol reacts readily here despite resisting the usual simple alcohol-oxidation test.
Separate the organic and aqueous layers using the approved settling and separating-funnel procedure. Use known composition and density evidence to identify the layer; do not rely on the claim that every organic liquid floats. Washing with hydrogencarbonate removes residual acid and releases carbon dioxide, so the controlled addition and careful venting steps matter.
A suitable drying agent removes traces of water from the separated organic phase. Remove that solid before distilling the liquid and collect the specified boiling fraction. The alcohol and chloroalkane have different intermolecular interactions: the alcohol can form extensive hydrogen bonds, while the chloroalkane cannot donate an O–H hydrogen bond. This helps explain their different boiling behaviour and water solubility.
A product portion can be hydrolysed under the approved conditions to release chloride, then appropriately acidified with nitric acid before silver nitrate is added. A white precipitate supports chloride release. Residual hydrochloric acid would also give chloride, so the purification and control evidence matter. Silver nitrate added to an unhydrolysed contaminated mixture is not a convincing standalone proof of the covalent product.
Use the limiting reactant and a 1:1 product ratio to find theoretical yield. A measured liquid volume needs the stated density to become mass. Low recovery can reflect transfer, volatility, incomplete reaction or product lost to washes. A high apparent mass can reflect water or starting material rather than excellent conversion. Compare boiling range and independent identity evidence with the yield.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: Why could residual HCl give a misleading positive product test with silver nitrate?
Purify the product and use the complete approved hydrolysis-and-test sequence with suitable controls.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.