Question:
I had a discussion with a colleague about an SCH4U ester lab I run. Typically I make available a number of carboxylic acids and alcohols and students choose a variety of esters to try and synthesize, smell and test the water solubility of.
My colleague’s concern was that the dehydration of methanoic acid is a competing reaction with the esterification and that non-trivial amounts of carbon monoxide could form when a combination of methanoic acid, alcohol and concentrated sulfuric acid is heated via boiling water bath in a test tube.
Any thoughts on the relative rates and hazards of methanoic esterification?
Response:
It is always good practice to examine the underlying chemistry and realistic safety implications of the reactions in SCH4U.
Your colleague is correct that concentrated sulfuric acid can dehydrate formic (methanoic) acid to carbon monoxide under certain conditions. However, given the reaction conditions, volumes and temperatures required for esterification, as well as ventilation requirements for science labs, the practical risk of CO exposure is extremely low. However, other concerning hazards posed by the use of formic acid (under esterification conditions) are more relevant.
Formic acid is flammable, corrosive, and has an elevated risk of explosion if heated under confinement (Fisher Scientific SDS Formic acid). These hazards significantly outweigh concerns of carbon monoxide production.
Additionally, given the necessary esterification conditions, this esterification reaction will be favoured compared to other competing reactions. (Yasaka et al, 2006).
In particular, the use of a water bath as a heat source is a critical safety control. Use of a water bath significantly reduces risk compared to a dry bath or a microwave, absorbs vapours produced during the reaction, and controls the temperature so it remains below the minimum 120 °C required for dehydration.
When planning any class activity, especially ones that involve chemical hazards, it is important to consider STAO’s Safety Triangle and learning goals. Namely, educators are asked to reflect on safer alternatives, reduced concentrations and reduced quantities.
Therefore, the more credible hazards in this experiment are associated with formic acid, sulfuric acid, flammables, heat, and pressure, as opposed to carbon monoxide.
A complex stoichiometry calculation of the potential CO concentration from emissions using volume of the classroom/fume hood, room occupancy and air exchange flow rate can be done to determine a more accurate threshold. If the concern persists, install and maintain a CO detector as a tool for an extension to learning.
In Summary:
The meaningful hazards are the chemicals and heat, as opposed to CO. In both microscale and standard test-tube procedures, the more likely risks are:
- Concentrated sulfuric acid – severe chemical burn hazard, violent dehydration of organics, strong heat generation when mixed
- Formic acid – corrosive, skin, eye, and respiratory hazard
- Alcohols- flammable, vapour ignition hazard
- Hot water baths and hot glassware, burn/scald risk
- Pressure capped or sealed test tubes
We hope that the information in this response will prove useful in helping you make informed decisions as to safety at your workplace. Please send feedback as to the quality of the response and response time. Feel free to contact us again on this topic as well as others.
References Cited:
Fisher Scientific. (2025, December 18). Safety Data Sheet: Formic acid (98 %), catalog no. AC147930250 [Safety data sheet]. Fisher Scientific. https://www.fishersci.com/store/msds?countryCode=US&language=en&partNumber=AC147930250&productDescription=FORMIC+ACID+98%25+25ML&vendorId=VN00033901
Yasaka, Y., Yoshida, K., Wakai, C., Matubayasi, N., & Nakahara, M. (2006). Kinetic and equilibrium study on formic acid decomposition in relation to the water-gas-shift reaction. Journal of Physical Chemistry A, 110(38), 11082–11090. https://doi.org/10.1021/jp0626768
Dated: January 2026