[bhushan]

i have prepared the hemihydrate and monohydrate and dihydrate compound.but how can know the compound is mon hemi or dihydrate ? please reply soon

[OC pro]

Karl-Fischer titration or thermo analysis.

[Agathiyar]

Karl-Fischer titration gives you percentage of water in your compound (Be aware that accurate weight of the compound transferred to the Karl-Fischer is very important, no human errors). Secondly XRD of each compound should show the number of water molecules it associate with.

[bhushan]

hiii agathiyar , you are correct, by KF we can find out % water in  compound,but on basis of that how can i say that my compound is monohydrate or hemihydrate ?
for example , if moisture is 2% in my compound then how can i find that it is monohydrate or dihydrate or hemihydrate ? i hope u understand my problem. reply

[MOTOBALL]

Suppose your cmpd. has MW M,

then for a semihydrate   M(0.5 H2O) the water % = [(0.5 x 18)/(M + 0.5 x 18)] x 100

Similarly for mono- and di-hydrates.

Compare your calculated %-water values to the measured values.

[bromidewind]

Couldn't you also use GC? I haven't done anything like this before, but I would imagine you could dissolve the compound in an appropriate solvent and run a GC. The only difference in the spectra would be water, and some integration could tell you the percentages.

[Agathiyar]

Hi Bhusan,

Motoball has written very nicely, first you have to have calculated value (theoretical value) of your compound as different hydrates.  Then do the actual analysis and find out the percentage of water, then match the value with your theoretical values. 
GC might not work out if your compound molecular weight is high, and here again you need to have standard solutions and internal standard, more work needed compared to Karl-Fischer method.

[bhushan]

MOTOBALL and agithar could we found out hemifumarte or difumarate compound in the same way as we found out the hemihydate or monohydrate or dihydrate compounds . reply

[orgopete]

hiii agathiyar , you are correct, by KF we can find out % water in  compound,but on basis of that how can i say that my compound is monohydrate or hemihydrate ?
for example , if moisture is 2% in my compound then how can i find that it is monohydrate or dihydrate or hemihydrate ? i hope u understand my problem. reply

If you have an organic compound and wish to know whether it is a mono, di, etc. hydrate, why not just send it out for microanalysis. I am presuming that you have a nice, dry, sharp melting, crystalline solid. Ask for the percent composition of all atoms present except oxygen. You should get a result within 0.3% of theo. Calculate the theoretical values to compare with results received.

[Agathiyar]

First take a clean nice 1H NMR of your sample having fumarate; compare the integration of one of the signal (for example methyl or something else) from your compound with one of the signal of fumarate.  Calculate the mole percentage of the fumarate, and then you can decide whether it is hemi, mono etc..,