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KBS17-3 - Propargylation of 1,6-diaminohexane #19
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##28.06.22
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29.06.22
Vial (empty) = 15.7175 NMR1H NMR (300 MHz, Chloroform-d) δ 4.02 (s, 4H), 3.30 (s, 4H), 2.17 (s, 2H), 1.58 (s, 4H), 1.45 (d, J = 7.2 Hz, 18H), 1.26 (s, 4H). KBS17-3 cr_1.zip All expected peaks are present but integrals are too large for results < 2 ppm. Potentially due to having 2 products (mono and bis) which have minimally different peaks in this zone - need to figure out what the mono product is expected to look like. |
30.06.22Decided to try and figure out what might be in the aqueous layer, as it was strongly coloured (reddish brown). pH was neutral (see image), so added NaOH (2.5 M) until it reached pH 11/12 (as tested by universal indicator strips) - wouldn't go higher even with addition of copious amounts of NaOH. Extracted with ethyl acetate (2 x 80 mL) and got a straw-coloured organic extract. Dried over MgSO4 and rotovapped down. First extraction with ethyl acetate |
15.07.22Tried and failed to rotovap down second extraction so dissolved in toluene (~ 5 mL) and washed with water (5 x 10 mL). Vial (empty): 15.7032 g NMRInitial NMR analysis (1H NMR, 300 MHz) indicates that coloured substance is product rather than starting material. |
20.07.22Columned crude product with upsetting results. First column produced 4 separate spots on TLC, each of which were collected separately. A - F 1-5 - 88 mg However, as the mass total was significantly less than the ~ 500 mg crude product, the column was washed again with another gradient. All fractions showing signs of product of any kind were collected as one "runoff" sample. Runoff = 176 mg NMR analysis of the samples indicated that A contained only solvent and nothing of interest. B contained something, but had no tell-tale Boc peak at 1.45 so didn't appear to be either SM or product. C was not analysed as there was too little. D contained a very small amount of material which appeared to be the same as the product seen in the Runoff sample - this material had a Boc peak and was not SM. The Runoff sample was then analysed via mass spec. This indicated the presence of the mono-propargylated product (377.24, [M+Na]) with only a tiny peak indicating that the bis-propargylated product might be present (393.23, [M+H]). NMR1H NMR (300 MHz, CDCl3) δ 4.53, 4.01, 3.29, 3.13, 3.09, 2.18, 1.46, 1.43, 1.21. LRMSF3-8 Empty vial: 15.7611 F9-24 Empty vial: 15.8789 |
20.07.22Ran off remainder of column (30 -100% ethyl acetate in hexane over 12 CV). F3-8 Empty vial: 15.7611 F9-24 Empty vial: 15.8789 |
25.07.22Ultimately only one product was isolated. This was identified as the mono-propargylated side product rather than the bis-propargylated product. It was recovered in a yield of 38% (175 mg, 0.494 mmol). This side product was carried on into #23. |
Link to HIRAC, original method and master page.
Next attempt is #22.
KBS17 Generic propargylation of 1,n-diamine.docx
Reaction scheme
Molecular weights
SM = 316.44
Product = 392.54
Predicted side product (mono-propargylated) = 354.49
Outcome
Only side product recovered (175 mg, 38%).
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