92
K. Igarashi and H. Ooshima
Three types of polymorphs have been reported for glycine. In cooling crystallization from the aqueous solution, metastable α-form and stable γ -form are obtained.
On the other hand, it is known that needle-like β-form is precipitated from an aqueous
alcohol solution. The β-form is the most unstable of the three polymorphs and
is known to change to metastable α-form by solvent-mediated transformation in
solution.
The polymorphs of the obtained crystals were identified by XRD. Figure 5.10
shows XRD profiles of glycine crystals obtained with different methanol compositions. The average residence time τ is 3.3 s. It can be seen that there is a difference
in the XRD pattern between the methanol composition of 50% and the others. The
α-form of glycine has characteristic peaks that are not found in other polymorphs at
2θ = 14.8°, 29.2°, 29.9°. In addition, the peaks peculiar to β-form appear at 17.9°,
33.8°, and 34.4°. From the results, it was found that α-form was obtained at 50%
methanol, and β-form was obtained at 73 and 91% (Table 5.2).
Fig. 5.10 XRD profiles of glycine crystals obtained with different methanol composition
Table 5.2 Summary of polymorphs of the glycine crystals obtained at different methanol
composition and residence time
Residence time τ (s)
Yield of crystals (%)
Glycine
l-alanine
0.33
102
87.2
3.3
101
89.1
33
92.5
98.8
K. Igarashi and H. Ooshima
Three types of polymorphs have been reported for glycine. In cooling crystallization from the aqueous solution, metastable α-form and stable γ -form are obtained.
On the other hand, it is known that needle-like β-form is precipitated from an aqueous
alcohol solution. The β-form is the most unstable of the three polymorphs and
is known to change to metastable α-form by solvent-mediated transformation in
solution.
The polymorphs of the obtained crystals were identified by XRD. Figure 5.10
shows XRD profiles of glycine crystals obtained with different methanol compositions. The average residence time τ is 3.3 s. It can be seen that there is a difference
in the XRD pattern between the methanol composition of 50% and the others. The
α-form of glycine has characteristic peaks that are not found in other polymorphs at
2θ = 14.8°, 29.2°, 29.9°. In addition, the peaks peculiar to β-form appear at 17.9°,
33.8°, and 34.4°. From the results, it was found that α-form was obtained at 50%
methanol, and β-form was obtained at 73 and 91% (Table 5.2).
Fig. 5.10 XRD profiles of glycine crystals obtained with different methanol composition
Table 5.2 Summary of polymorphs of the glycine crystals obtained at different methanol
composition and residence time
Residence time τ (s)
Yield of crystals (%)
Glycine
l-alanine
0.33
102
87.2
3.3
101
89.1
33
92.5
98.8