Basicity of Amidines and Guanidines

Amidines and guanidines are organic compounds with the chemical formula of RC(NR)NR2 and  HNC(NH2)2 respectively. In case of amidines R group can be same or different,  they are generally referred to as the imine derivatives of amides. Guanidines are colourless that can dissolve in polar solvents, because of the strong basicity of guanidines they are used in the production of plastics and explosives. Guanidines are also found in urine as production of protein. Because of the resonance stability and efficient solvation by water molecule, guanidines are more basic than amidines as a result the pkb value found to be 13.6 which indicates or confirms that guanidines are more basic than amidines.

• Amidines and guanidines 

Amidines are chemical compounds with the functional group RC(NR)NR2 and one or more R groups. They are amides’ imine derivatives (RC(O)NR)2. Formamidine, HC(=NH)NH2, is the most basic amidine. Whereas guanidines are colourless that can dissolve in polar solvents, because of the strong basicity of guanidines they are used in the production of plastics and explosives. Guanidines are also found in urine as production of protein. Because of the resonance stability and efficient solvation by water molecule, guanidines are more basic than amidines as a result the pkb value found to be 13.6 which indicates or confirms that guanidines are more basic than amidines. 

• Structure of Amidines and guanidines 

Guanidine is a nitrogen-containing derivative of carbonic acid. That is, each OH is replaced by an NH2 group, and the C=O group in carbonic acid is replaced by a C=NH group. Similarly, isobutylene can be thought of as the carbon analogue. Despite the molecule’s simplicity, a detailed crystallographic examination of guanidine was completed 148 years after its first synthesis. Single-crystal neutron diffraction was used to precisely measure the locations of hydrogen atoms and associated displacement parameters in 2013. 

Depending on the temperature, solvent, and structure of the primary amine, condensation with N,N-dimethylacetamide dimethyl acetal generates a mixture of acetamidine and imidate ester.

• Basicity of amidines and guanidines

Amidines are more basic than amines because protonation occurs of the sp2 hybridised nitrogen. This happens because the positive charge can be delocalised onto both nitrogen atoms. The cationic species that results is known as an amidinium ion, and it has identical C-N bond lengths. 

Guanidine is a strong base with a pKb of 0.4. The conjugate acid is present in the majority of guanidine derivatives.

The guanidinium cation (C(NH2)3+) is the conjugate acid. This planar, symmetric ion is made up of three amino groups, each of which has a covalent link of order 4/3 with the centre carbon atom. Because of the effective resonance stabilisation of the charge and efficient solvation by water molecules, it is a highly stable +1 cation in an aqueous solution. As a result, its pKaH is 13.6, indicating that guanidine is a highly strong base in water, existing almost completely as guanidinium in neutral water.

Why are guanidines more basic than amidines?

Because of the presence of resonance stability and due to efficient solvation by water, its pkb value comes out to be 13.6, which indicates guanidines is a very strong base compared to amidines.

Methylamine is more reactive toward nucleophilic reaction because it lacks any resonance stability.

• Properties and application of amidines and guanidines

Amidine substituents are found in several drugs and therapeutic prospects. Antiprotozoal Imidocarb, insecticide amitraz, anthelmintic tribendimidine, and xylamidine, are all examples.

In perovskite solar cells, formamidinium (see below) can be treated with a metal halide to form the light-absorbing semiconducting substance. In photovoltaic systems, formamidinium (FA) cations or halides may partially or completely replace methylammonium halides in forming perovskite absorber layers.

Guanidinium chloride is a now-debatable adjuvant in botulism treatment. Recent investigations have revealed that a significant percentage of individuals do not improve after taking this medication. At physiological pH, guanidine exists protonated as guanidinium in solution.

Guanidinium chloride (also known as guanidine hydrochloride) is used to denature proteins because of its chaotropic characteristics. Guanidinium chloride denatures proteins in a linear connection between concentration and unfolding free energy. Almost all proteins lose their secondary structure and become randomly coiled peptide chains in aqueous solutions containing 6 M guanidinium chloride. 

Conclusions

Amidines and guanidines are organic compounds having the chemical formula of RC(NR)NR2 and  HNC(NH2)2, respectively. In the case of Amidines, the R group can be the same or different. They are generally referred to as the imine derivatives of amides. Because of the resonance stability and efficient solvation by a water molecule, guanidines are more basic than amidines. As a result, the pkb value was found to be 13.6, which indicates or confirms that guanidines are more basic than amidines. Both have many applications in medicine, such as Guanidine, the primary antihyperglycemic component in French lilac, which has been used to treat diabetes in Europe since the Middle Ages. After discovering insulin, further research for blood sugar regulation was temporarily halted due to its long-term hepatotoxicity. Amidine substituents are found in several drugs and therapeutic prospects. Antiprotozoal Imidocarb, insecticide amitraz, anthelmintic tribendimidine, and xylamidine, are all examples.