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Solvents, Recrystallization, and Melting Point

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Presentation on theme: "Solvents, Recrystallization, and Melting Point"— Presentation transcript:

1 Solvents, Recrystallization, and Melting Point

2 Intermolecular Forces
Hydrogen bonding Acceptor/donor Dipole/dipole Dipole/induced dipole Induced dipole/induced dipole Also called London dispersion forces VDWs Forces

3 General Principles If molecules are about the same mass
H-bonding > Dipole-dipole > Induced dipole Induced dipole is weakest interaction, but as surface area increases, cumulative effect can overcome stronger IMF Strategy for predicting relative boiling points

4 Solvents and Boiling Points
Ether (diethyl ether) Dichloromethane (methylene chloride) acetone methanol Tetrahydrofuran (THF) 35 oC 40 oC 56 oC 65 oC 66 oC hexanes Ethyl acetate (EtOAC) ethanol acetonitrile water 69 oC 77 oC 78 oC 82 oC 100 oC toluene Pyridine (pyr) Acetic acid Dimethyl formamide (DMF) Dimethylsulfoxide (DMSO) 111 oC 115 oC 118 oC 153 oC 189 oC

5 H-Bond Donor, Acceptor, Neither, or Both
Ether (diethyl ether) Dichloromethane (methylene chloride) acetone methanol Tetrahydrofuran (THF) 35 oC 40 oC 56 oC 65 oC 66 oC hexanes Ethyl acetate (EtOAC) ethanol acetonitrile water 69 oC 77 oC 78 oC 82 oC 100 oC toluene Pyridine (pyr) Acetic acid Dimethyl formamide (DMF) Dimethylsulfoxide (DMSO) 111 oC 115 oC 118 oC 153 oC 189 oC

6 Polar Protic, Polar Aprotic, Nonpolar
Ether (diethyl ether) Dichloromethane (methylene chloride) acetone methanol Tetrahydrofuran (THF) 35 oC 40 oC 56 oC 65 oC 66 oC hexanes Ethyl acetate (EtOAC) ethanol acetonitrile water 69 oC 77 oC 78 oC 82 oC 100 oC toluene Pyridine (pyr) Acetic acid Dimethyl formamide (DMF) Dimethylsulfoxide (DMSO) 111 oC 115 oC 118 oC 153 oC 189 oC

7 Solubility “Like dissolves like” Based on IMF

8 Solubility Rules of Thumb
Water soluble if one H-bond donor per 3C Water soluble if ionic and less than 8C Water soluble if small, highly polar

9 Lab 2a: Purification of Biphenyl by Recrystallization
Question: What solvent can be used for an effective recrystallization of biphenyl? How well does recrystallization work as a purification?

10 Applying Solvents and Intermolecular Forces
Purification: separation of target compound from impurities Characterization Identity: Do I have what I think I have? Purity: How pure is the compound?

11 Recrystallization Purification for solids Useful for
Large samples Final purification step Based on differential solubility

12 Practical Aspects Impure Solid  Dissolve Recrystallize Filter
then watch the Chapter 15 video of recrystallization from mixed solvent

13 Recrystallization: Theory
IMF in solids Temperature dependence Equilibrium process in slow crystal formation

14 Important Points Choice of solvent Mixed solvents
Maintaining hot solvent Safety when boiling Hot filtration Inducing crystallization Washing crystals Too much/too little solvent Oiling out

15 Melting Point Physical property to characterize substance Identity
purity capillary Melt-temp then watch the Chapter 14 video of packing a capillary tube for melting point

16 Theory and Application
Pure crystals and impure crystals Intermolecular Forces Lattice energy Application Depressed MP Broad MP Mixed MP Eutectic mixture

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