Molecular Techniques and Methods

Physical Properties of Solvents

Copy Right © 2001/ Institute of Molecular Development LLC

Miscibility numbers (M-numbers) are used to predict the miscibility of a liquid with one of the standard solvents. To determine the miscibility of the two liquids, subtract the smaller value from the larger.

  • If the difference between the two M-numbers equals 15 or less, the two liquids are miscible in all proportions at 15oC.
  • A difference of 16 units shows that the two liquids possess a critical solution temperature between 25 and 75oC, with 50oC as the optimal temperature.
  • If the difference equals 17 or more, the two liquids are immiscible, or their critical solution temperature is above 75oC.

  • Interaction between the molecules of the two liquids can sometimes change the expected degree of miscibility. For example, ethers or tertiary amines show unpredicted miscibility with hydroxylic solvents due to hydrogen bonding. Unusually strong hydrogen bonding is also responsible for the miscibility of long-chain alcohols or carboxylic acids with standard solvents of low M-number. Conversely, they show anomalous immiscibility with aprotic solvents of low M-number. Some solvents prove immiscible with solvents at both ends of the lipophilicity scale.

  • Polarity Index
    Solvent
    Boiling Point oC (1 atm)
    Miscibility Number (M)
    0.0
    Hexane
    68.7
    29
    0.0
    Cyclohexane
    80.7
    28
    0.3
    n-Decane
    174.1
    29
    0.4
    Octane
    99.2
    29
    1.7
    Butyl ether
    142.2
    26
    1.8
    Triethylamine
    89.5
    26
    2.2
    i-Propyl ether
    68.3
    26
    2.3
    Toluene
    101.6
    23
    2.4
    p-Xylene
    138.0
    24
    3.0
    Bezene
    80.1
    21
    3.3
    Benzyl ether
    288.3
    26
    3.4
    Methylene chlororide
    39.8
    20
    3.4
    Cloroform
    61.2
    19
    3.7
    Ethylene chloride
    83.5
    20
    3.9
    i-Butyl alcohol
    117.7
    15
    4.2
    Tetrahydrofuran
    66.0
    17
    4.3
    Ethyl acetate
    77.1
    19
    4.3
    1-Propanol
    97.2
    15
    4.3
    2-Propanol
    117.7
    15
    4.4
    Methyl acetate
    56.3
    15/ 17
    4.5
    Methyl ethyl ketone
    80.0
    17
    4.5
    Cyclohexanone
    155.7
    17
    4.5
    Nitrobezene
    210.8
    14/ 20
    4.6
    Benzonitrile
    191.1
    15/ 19
    4.8
    p-Doxane
    101.3
    17
    5.2
    Ethanol
    78.3
    14
    5.3
    Pyridine
    115.3
    16
    5.3
    Nitroethane
    114.0
    13/ 20
    5.4
    Acetone
    56.3
    15/ 17
    5.5
    Benzyl alcohol
    205.5
    13
    5.7
    Methoxyethanol
    124.6
    13
    6.2
    Acetonitrile
    81.6
    11/ 17
    6.2
    Acetic acid
    117.9
    14
    6.4
    Dimethylformamide
    153.0
    12
    6.5
    Dimethylsulfoxide
    189.0
    9
    6.6
    Methanol
    64.7
    12
    7.3
    Formamide
    210.5
    3
    9.0
    Water
    100.0
    -


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