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I'm doing a project for school and I need to convert salicyl alcohol to salicylic acid, but I'm not allowed to use $\ce{CrO3}$ because of its toxicity. I know it is also possible to oxidize a primary alcohol to a carboxylic acid with potassium permanganate, but I read it might be a too strong oxidizer. Is there any good alternative?

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    $\begingroup$ @IvoFilot Please don't use something like CrO$_3$ as it may break in some browsers (especially with the responsive design); instead use the mhchem macro $\ce{CrO3}$. More detail on meta: here and here. We also usually do not correct Brittish spellings (if used consistently), because that has lead to edit wars in the past. In any case: Thanks for your effort. $\endgroup$
    – Martin - マーチン ♦
    Nov 13, 2018 at 14:14
  • $\begingroup$ Hmm, I think there are too many ways... $\endgroup$
    – Mithoron
    Nov 13, 2018 at 19:38

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@Waylander: A general Procedure given in J. Org. Chem. 1999, 64(7), 2564–2566 as follows:

Typical Procedure. A mixture of alcohol 1 ($\pu{40 mmol}$), TEMPO ($\pu{436 mg}$, $\pu{2.8 mmol}$), $\ce{MeCN}$ ($\pu{200 mL}$), and sodium phosphate buffer ($\pu{150 mL}$, $\pu{0.67 M}$, $\pu{pH = 6.7}$) is heated to $\pu{35 °C}$. Then mixtures of $\pu{9.14 g}$ of 80% sodium chlorite ($\ce{NaClO2}$, $\pu{80.0 mmol}$) in $\pu{40 mL}$ of water and 2.0 mol% dilute bleach ($\pu{1.06 mL}$ of 5.25% $\ce{NaOCl}$ diluted into $\pu{20 mL}$ with water) are added simultaneously over $\pu{2 h}$ (Caution! Do not mix bleach and $\ce{NaClO2}$ before being added to the reaction mixture). The mixture is stirred at $\pu{35 °C}$ until the reaction is complete (<2% starting material, $\pu{2−5 h}$ reaction time), then cooled to room temperature. Water ($\pu{300 mL}$) is added, and the $\mathrm{pH}$ is adjusted to $8.0$ with $\pu{2.0 N}$ $\ce{NaOH}$ (about $\pu{48 mL}$). The reaction is quenched by pouring into cold ($\pu{0 °C}$) $\ce{Na2SO3}$ solution ($\pu{12.2 g}$ in $\pu{200 mL}$ of water) maintained at $\pu{<20 °C}$. The $\mathrm{pH}$ of the aqueous layer should be $8.5$−$9.0$. After stirring for $\pu{0.5 h}$ at room temperature, methyl tert-butyl ether (MTBE, $\pu{200 mL}$) is added. The organic layer is separated and discarded. More MTBE ($\pu{300 mL}$) is added, and the aqueous layer is acidified with $\pu{2.0 N}$ $\ce{HCl}$ (~$\pu{100 mL}$) to $\pu{pH = 3−4}$. The organic layer is separated, washed with water ($2 \times \pu{100 mL}$) and brine ($\pu{150 mL}$), and then concentrated to give the crude carboxylic acid 2 in 85−100% yield. The products may be purified by silica gel column chromatography or crystallization.

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Converting alcohol to carboxylic acid requires strong oxidizing agent and those reagents are not commonly in school laboratory. In that case, mild oxidizing agent should be used to first convert salicyl alcohol to salicylaldehyde and then convert to salicylic acid.

You should try $\ce{MnO2}$ or (Conc. $\ce{HCl}$, ethyl acetate, sodium Hypo (8 - 12%)) and then use $\ce{KMnO4}$ to convert it to salicylic acid.

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