| LAB NOTES | |
Rules / Lab TechniquesRULESTo help keep the lab functional, please follow the following guidelines. These are all just common sense and common courtesy rules, but everyone needs to be reminded of them. All group glassware (flash columns, schlenkware, distillation heads, etc.) must be cleaned and returned immediately after use. Group equipment (syringe pump, portable pump, balances, etc.) must be cleaned and made available within a reasonable time. Traps on the vacuum pumps must be cleaned out if solvents are pumped in. Chemicals should not be hoarded at the bench. Unique chemicals may be kept for a reasonable time, but common reagents should be returned to the shelves. If you use all or close to all of a chemical, you must see that it is reordered or replaced from the stockroom. Accidents happen, but be careful !!! If you break something, especially group equipment, repair it immediately. If you make a mess, clean it up. Rotovaps must left clean for the next user. Rinse the bump trap immediately after you use it. Glassware is much easier to clean if it is done immediately after use. Gastight syringes are very expensive and must be treated carefully. They must not be cleaned in acid or base baths as this will destroy the plunger. Be considerate to your labmates and help keep the lab workable !!!
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LAB TECHNIQUES |
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TITRATIONSIndicators to use for organometallic reagents in polar solvents when back titrating with a stock solution such as 1 M s-butanol in xylene: Stoichiometric indicators for organometallic reagents: 2,5-dimethoxybenzyl alcohol See: E. Juaristi J. Org. Chem. 1983, 48, 2603. Titrate THF or ether solutions of lithium aluminium hydride with 9-fluorenone.
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DRYING AGENTSSolvent Pretreatment Desiccant For desiccant efficiencies in drying alcohols, see: R. Smithers J. Org. Chem. 1983, 48, 2420. See also: Purification of Laboratory Chemicals, D. D. Perrin and W. L. F. Armarego, Pergamon, London, 1989.
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WORKUP OF ALUMINUM BASED REDUCTIONSA. To workup a reaction containing x g lithium aluminum hydride: B. Ethyl acetate is a good reagent to quench lithium aluminum hydride reductions since the resultant ethanol is easy wash out. C. To workup a reaction containing x mmol of an agent such as Dibal:
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WORKUP TO REMOVE SOLVENTSDioxane, DMF, DMSO, and THF reaction solvents are all readily removed by aqueous workup rather than distillation. Add reaction mixture to solvent such as ether and wash five times with water. Changes must be made if desired product is soluble in water or insoluble in ether.
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WORKUP TO REMOVE AMINESAcidic: Wash with 10% aqueous HCl solution.
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WORKUP TO REMOVE ORGANOTIN RESIDUESByproducts of tin based reactions such as Bu3SnBr can be removed by treatment with AlMe3 to create the nonpolar Bu3SnMe or NaOH to create the polar Bu3SnOH. See: P. Renaud, E. Lacote, L. Quaranta Tetrahedron Lett. 1998, 39, 2123.
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WORKUP TO REMOVE METAL SALTSMany transition metals can be removed by precipitation of the sulfides. Wash with aqueous sodium sulfide. If necessary, adjust pH to create H2S. Some transition metals can be removed by aqueous extraction with tris(hydroxymethyl)phosphine. See: R. H. Grubs Tetrahedron Lett. 1999, 40, 4137.
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HEATING BATHSWater Usable to about 80oC Mineral Oil Usable to about 150oC Silicone Oil Usable to about 250oC Phosphorous acids Usable to about 250oC (20% H3PO3, 80% H3PO4) Wood's Metal Usable to about 350oC (50% Bi, 25% Pb, 12.5% Sn, 12.5% Cd) Sand Usable to about 1000oC
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CLEANING BATHSGeneral Bath to Remove Organic Residues: Acid Bath: Chromic Acid Bath: (Due to environmental concerns, this is a last choice. However, the solution can be reused many times, thus minimizing what is washed down the drain.) |