Spectroscopic studies of carbohydrates. 1. The action of sulphuric acid on sugars

Microporous Humins Synthesized in Concentrated Sulfuric Acid Using 5-Hydroxymethyl Furfural

A new class of highly porous organic sorbents called microporous humins is presented. These microporous humins are derived from sustainable and industrially abundant resources, have high heat of CO₂ sorption, and could potentially be useful for the separation of carbon dioxide from gas mixtures. Their synthesis involves the polymerization of 5-hydroxymethyl furfural (HMF) in concentrated sulfuric acid and treatment with diethyl ether and heat. In particular, the porosities were tuned by the heat treatment. HMF is a potential platform chemical from biorefineries and a common intermediate in carbohydrate chemistry. A high uptake of CO₂ (up to 5.27 mmol/g at 0 °C and 1 bar) and high CO₂-over-N₂ and CO₂-over-CH₄ selectivities were observed. The microporous humins were aromatic and structurally amorphous, which was shown in a multipronged approach using ¹³C nuclear magnetic resonance and Fourier transform infrared spectroscopies, elemental analysis, and wide-angle X-ray scattering.

Standardization of a colorimetric method for the determination of fructose using o-cresol: Sulphuric acid reagent

Fructose developed a pinkish orange chromogen on treatment with o-cresol: 70% sulphuric acid at 32°C for 15 minutes with a λ max of 500nm. Fructose was 185 times more chromogenic than glucose. Total carbohydrate and fructose values in protein-free filtrate of normal serum samples were in the range, 55.4-86.3 mg/dl and 1.55-3.29 mg/dl, respectively. In diabetes, the observed values were 197-354 mg/dl and 2.91-6.81 mg/dl, respectively.

Further studies on the mechanism of phenol-sulfuric acid reaction with furaldehyde derivatives

Even though the chromogens formed from mannose and galactose showed comparable absorbances at 480 nm in the conventional (developer present during heat of dilution) and modified (developer reacted at room temperature after cooling; epsilon mannose = 13,700, galactose = 14,000) phenol-sulfuric acid reactions, shoulders in the region 420-430 nm were prominent in the former method. Fucose was 10 times less reactive in the modified method (epsilon = 800) than in the conventional method. 2-Formyl-5-furan sulfonic acid reacted equally efficiently in the two methods (epsilon = 40,800). 5-Methyl-2-furaldehyde, unlike the sulfonate derivative or 5-hydroxymethyl-2-furaldehyde, required heat for condensation with phenol. 2-Furaldehyde dimethylhydrazone reacted 25 times better to form a chromogen (epsilon = 40,500) in the modified phenol-sulfuric acid method. The possible roles of intermediates between hexoses and furaldehydes in forming chromogens and the effect of substitution at the 2- and 5-positions of furaldehyde on the rates of condensation with phenol for the observed differences between the conventional and the modified methods are discussed.

Reevaluation of the phenol-sulfuric acid reaction for the estimation of hexoses and pentoses

Evidence is provided to show that in the conventional phenol-sulfuric acid reaction procedure, phenol underwent sulfonation in situ and the phenolsulfonic acid formed decreased the color intensity for hydroxymethyl furfural (HMF), furfural, and many hexoses and pentoses tested. A modified method is described to overcome this problem in which phenol was added after the dehydration of carbohydrates by sulfuric acid and after cooling the system. The color intensity around 475-485 nm for different compounds was fairly proportional to the amount of furfural derivatives (absorption at 310-320 nm) formed from the sugars in the modified method unlike in the conventional procedure. The studies also show that for condensation of HMF derivatives with phenol, heat is not necessary. The color intensity in the modified method also increased compared to that in the conventional method. The increase in the modified method compared to that in the conventional method was 6.0-fold for furfural, 9.1-fold for hydroxymethyl furfural, 3.7-fold for fructose, 2.3-fold for xylose, and 2.0-fold for glucose and arabinose. The possible reasons for this differential increase are discussed.