Making the Smell of Rain

The video begins with the chemist's quest to recreate the earthy smell of rain, known as petrichor, in a lab setting. The primary molecule responsible for this scent is identified as geosmin. The chemist embarks on a journey to synthesize geosmin, starting with researching its chemical structure and potential methods for production. The process involves complex chemical reactions, beginning with the synthesis of ethyl vinyl ketone, a crucial reagent. The chemist meticulously sets up a reaction using hexanes, diethyl ketone, ethylene glycol, and p-Toluenesulfonic acid as a catalyst, employing a Dean-Stark apparatus to continuously remove water formed during the reaction. This step is crucial for driving the reaction to completion and achieving a successful synthesis of ethyl vinyl ketone.

This paragraph delves deeper into the synthesis of ethyl vinyl ketone, detailing the use of a Dean-Stark apparatus to facilitate the reaction between diethyl ketone and ethylene glycol. The chemist explains the importance of continuously removing water to avoid equilibrium and ensure product formation. After an 8-hour reaction, the presence of water confirms the success of the synthesis. The chemist then proceeds to the next step, involving the addition of bromine to the reaction mixture, which is carefully controlled to prevent side reactions. The reaction's completion is indicated by the disappearance of the orange color from the mixture. Subsequent extraction and purification steps yield a significant amount of the mono-brominated product, setting the stage for further reactions.

The chemist continues the synthesis process by focusing on the production of ethyl vinyl ketone. After preparing the mono-brominated product, the next steps involve the use of methanol and potassium hydroxide to create a potassium methoxide solution. This solution is crucial for the subsequent reaction with the mono-brominated product. The chemist carefully controls the reaction conditions, including temperature and solvent choice, to facilitate the formation of the desired vinyl product. The product is then purified through a series of extractions and distillations, ultimately yielding a clear liquid with a strong, distinctive smell reminiscent of turpentine or glue. The chemist emphasizes the importance of storing this product due to its stability and potential use in future reactions.

This paragraph describes the continuation of the geosmin synthesis process, starting with the preparation of 2-methylcyclohexanone and (S)-(-)-α-methylbenzylamine. The chemist uses a Dean-Stark apparatus to facilitate the reaction between these two compounds, forming an imine product. The reaction is monitored by the collection of water, indicating the progress and completion of the reaction. The product is then subjected to a Michael addition reaction with ethyl vinyl ketone, catalyzed by the enamine form of the imine. The resulting product is further processed through hydrolysis and extraction, leading to the formation of a diketone product. The chemist meticulously manages each step, ensuring the correct conditions for each reaction to proceed efficiently.

The chemist proceeds with the synthesis of geosmin by cyclizing the diketone product into a cyclic compound. This step involves the use of a base to catalyze the reaction, leading to a fused ring system through an aldol condensation, a type of Robinson annulation. The resulting product is then subjected to a Prilezhaev epoxidation, where an alkene double bond reacts with a peroxy acid to form an epoxide. The chemist carefully manages the reaction conditions, including the use of sodium bicarbonate to counteract the acidity of the perbenzoic acid. The product is purified through a series of washes and extractions, ultimately yielding a sweet and floral-smelling compound.

The final steps in the synthesis of geosmin involve a series of reductions and reactions to form the desired compound. The chemist uses lithium aluminum hydride to reduce the ketone and epoxide groups to alcohols, followed by the formation of a tosylate group. The tosylate is then reduced to a hydrogen, yielding geosmin. The chemist carefully manages the reaction conditions and purification steps, including the use of column chromatography and short path vacuum distillation. The final product is a fluffy white solid with an earthy, rain-like smell. The chemist notes the need to dilute the pure geosmin to better mimic the natural scent of rain and offers viewers the opportunity to experience the scent by supporting the project financially.