How To Improve Your Yield

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A number of common errors contribute to the majority of lowreaction yields. Compound can be lost through careless reaction procedure, during post-reaction manipulations or through decomposition. Yields will improve with practice, but some advice should also help.

  1. The Setup

    Flame dry or oven dry flask and stirbar
    Use clean glassware
    Calculate and weigh reagent amounts accurately
    Purify reagents and solvents, if necessary
    Be sure your reactant is pure
    Rinse (3 times with reaction solvent) flasks and syringes used to transfer reactant and reagents.

  2. The Reaction (TIME-SENSITIVE)

    Add reagents dropwise if necessary
    Continuously stir thoroughly
    Carefully keep temperature of reaction and liquid reagents at the correct level during addition and reaction
    Monitor your reaction carefully throughout the experiment.

  3. Quench (TIME-SENSITIVE)

    Quench your reaction exactly when it is complete, not before andnot hours afterwards, and quench carefully.
    note 1note 2

  4. Workup (TIME-SENSITIVE)

    Rinse flask (3 times) and stir bar with solvent
    Use enough solution (organic and aqueous) to ensure that solution is homogenous.
    Rinse separatory funnel after workup
    If you need a break, take it while your compound is being dried after workup.
    Rinse drying agent thoroughly (at least 3 times)
    If your compound is volatile, be careful with rotoevaporation.
    Beware of bumping on rotovap
    If possible, store your compounds neat, at low temperature.

  5. Purification

    Always transfer neat compound with pipette to prevent spillage
    If your compound is acid sensitive, be careful during silicachromatography
    Rinse test tubes after chromatography
    If your compound is volatile, be careful with vacuum pumps.
    Beware of bumping on rotovap
    If possible, store your compounds neat, at low temperature.



Tips from Site Visitors

Try this... Will this work? Percent who agree
When modifying a compound by way of an unpublished or largely undocumented procedure, be careful about solvent selection. Start with small amounts of the compound and test with various solvents until ones that work are found. Choose a solvent that won't engage in a competing reaction. For example don't use an alcohol with an acid anhydride or the main reaction may become esterification of the alcohol. yes no 96%
Be careful with the suggestion in Step I regarding reagent transfer by syringe. To my knowledge, most syringes are calibrated to deliver. This means that if you have 0.250mL (no bubbles) in a syringe and depress the plunger fully, you will transfer 0.250mL. If you use reaction mixture to rinse the syringe or pull the plunger up and down to squirt out the liquid that remains, you'll introduce excess reagent that was in the tip of the syringe barrel and in the needle. A quick calculation revealed that a 6%94 18-gauge needle has an approximate volume of 84 microliters. That%92s a significant excess if you%92re working on millimolar scale or less. yes no 94%
Avoid transferring chemicals to different glassware as much as possible, particularly if you're working on small scales - you can lose a lot of product if you're constantly having to change flasks, etc. (For this reason, make sure you use tared flasks so you can weigh your product easily.) yes no 91%
when performing column chromatography always start with a nonpolar solvent and gradually increase the polarity gradient. This helps in effective seperation of the product from the embedded impurities. yes no 83%
. yes no 80%
Perform the experiment in polar conditions (T %3C -50 degrees) to improve yield. Make sure to wear thick gloves! yes no 20%
Rather than directly pouring out an organic layer that needs to be dried with a drying agent, add the drying agent directly to the seperatory funnel and plug the bottom of the funnel with cotton kept in a dessicator. This will save time as well as increase yield. yes no 9%

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