Grignard synthesis of triphenylmethanol theoretical yield

M31_LEHM3752_02_SE_C30.QXD Experiment 30 2/28/08 5:26 PM Page 269 Synthesis of Triphenylmethanol and the Trityl Carbocation Synthesis of Triphenylmethanol and the Trityl Carbocation Reactions of Carbonyl Compounds. Reactions of Organic Halides. Preparation of Alcohols. Nucleophilic Addition. Organometallic Compounds. Carbocations. Infrared Spectrometry. Operations OP-12 OP-7 OP-10 OP-11 OP-14 OP-15 OP-16 OP-17 OP-19 OP-24 OP-25 OP-26 OP-28 OP-33 OP-39 Excluding Water from Reaction Mixtures Heating Mixing Addition of Reactants Trapping Gases Gravity Filtration (SS) Vacuum Filtration Centrifugation (µS) Evaporation Washing Liquids Drying Liquids Washing and Drying Solids Recrystallization Melting Point Infrared Spectrometry (optional) Before You Begin 1. Read the experiment and operation OP-12, read or review the other operations as necessary, and write an experimental plan. 2. Calculate the mass of 22.0 mmol (SS) or 4.00 mmol (µS) of magnesium, the mass of 20.0 mmol (SS) or 3.80 mmol (µS) of benzophenone, the mass and volume of 22.0 mmol (SS) or 4.00 mmol (µS) of bromobenzene, and the theoretical yield of triphenylmethanol. Calculate the theoretical yield of trityl fluoborate from 1.00 g (SS) or 0.100 g (µS) of triphenylmethanol. Scenario The Complementary Colors Company manufactures synthetic dyes, including a number of triphenylmethane dyes. Gilda Lillie, product development director for the company, would like to develop some new colors to improve its market share in the dye industry. She has learned, for example, that having two para-dimethylamino groups on two of the three benzene rings in the parent structure yields a green dye (Malachite Green), while having three of them yields a violet dye (Crystal Violet). 269 EXPERIMENT 30 M31_LEHM3752_02_SE_C30.QXD 2/25/08 2:13 PM 270 Page 270 Part II Correlated Laboratory Experiments NMe2 Me2N C + Cl– carbocation structure NMe2 + Me2N C Cl– iminium ion structure Two resonance structures for Malachite Green, a triphenylmethane dye C + BF4– triphenylmethyl (trityl) fluoborate The company’s technicians need to know how the kinds and positions of substituents on the parent triphenylmethyl ring structure affect the color of triphenylmethane dyes. For that, they need a sample of the unsubstituted parent compound of these dyes, the triphenylmethyl (trityl) carbocation. Your assignment is to prepare triphenylmethanol and convert it to trityl fluoborate, a salt that contains the trityl carbocation. Applying Scientific Methodology The main scientific problem—determining the color of trityl fluoborate— will be solved when you prepare this substance. The Colorful Career of the Triphenylmethanes The synthesis of quinine was not accomplished until 1944—88 years after Perkin had attempted it. Reduced form of malachite green NMe2 Me2N C H Key Concept: When a substance cannot be represented satisfactorily by a single structural formula, its actual structure is regarded to be a composite of two or more contributing structures. During his Easter vacation from London’s Royal College of Chemistry, 18-year-old William Perkin was trying to synthesize quinine when he came up with an unpromising red-brown solid that had none of the properties of quinine. Undeterred, Perkin used similar methods to synthesize mauve, a light purple dye whose commercial success launched the synthetic dye industry. The first triphenylmethane dye, fuchsin, was synthesized a few years later, and it was followed soon after by Malachite Green, Crystal Violet, and other triphenylmethane dyes. The race to develop commercially marketable dyes also stimulated research into the molecular basis of color. Why, for example, is Malachite Green green and its reduced form colorless? The chromophore of a compound is the part of its molecule over which electrons can be delocalized and which is responsible for its absorption of ultraviolet or visible light. Triphenylmethane dyes come in all colors of the rainbow, from the red of rosaniline through Malachite Green and Victoria Blue to Crystal Violet. The chromophores responsible for these colors appear to be nitrogen-substituted triphenylmethyl (trityl) cations, but they are not true carbocations because most of their positive charge is distributed to the nitrogen atoms, as in the iminium ion form of Malachite Green shown previously. According to resonance theory,