Rethink Teaching Laboratories using the lens of green chemistry: reducing Hazardous solvents

1. Context and Scientific-Educational Rationale

Academic laboratories generate thousands of metric tons of hazardous chemical waste each year, the majority of which is incinerated at high temperatures, releasing carbon and chlorine into the atmosphere. Among the most widely used organic solvents, dichloromethane (DCM) has historically been employed for reactions, extractions, and chromatographic purifications. However, the use of DCM poses severe health and environmental concerns:

·        Toxicity and Health Hazards: DCM is classified by IARC as a Group 2A carcinogen. Exposure via inhalation or skin contact causes central nervous system depression and liver damage. In the human body, DCM is metabolized into potent toxins such as formaldehyde, formyl chloride, and carbon monoxide, and it has been responsible for numerous documented fatalities in occupational settings.

·        Environmental Impact: DCM is a very short-lived substance (VSLS) that contributes to stratospheric ozone depletion and has been detected as a pollutant in groundwater, soil, and drinking water.

·        Strict Regulatory Landscape: Recent 2024 US EPA regulations under the Toxic Substances Control Act (TSCA) and the Workplace Chemical Protection Program (WCPP) mandate frequent environmental monitoring (every 3 months) and impose high compliance costs, prompting educational institutions to eliminate DCM.

·        Impact of Chromatography: Column chromatography consumes large amounts of solvent per gram of purified product; replacing DCM in this specific teaching lab technique allows for a significant reduction in toxic waste generation.

·        Solvent Categorization (CHEM21): According to the CHEM21 solvent selection guide, DCM and hydrocarbons such as hexane are categorized as hazardous solvents to avoid, whereas ethyl acetate is listed as a recommended/preferred solvent due to its lower toxicity and reduced environmental impact.

2. Project Objectives

·        Green Chemistry Integration: Teach students to evaluate the toxicological and environmental impacts of solvents when designing chemical procedures.

·        Hazardous Waste Reduction: Redesign part of the traditional laboratory exercise to reduce the use and disposal of harmful halogenated solvents.

·        Experimental and Pedagogical Validation: Demonstrate that the eco-friendly Cyclohexane / Ethyl Acetate mixture provides analytical and separation performance equivalent to DCM for purifying organic mixtures on silica columns.

·        Academic Community Awareness: Share the quantitative results obtained with students and faculty during EWWR 2026.

3. Experimental Procedure Description

·        Target Audience: 18 student groups in a Medicinal Chemistry course (52 students total).

·        Laboratory Task: Column chromatography purification on silica gel of a model mixture containing two organic compounds with different polarities.

·        Group Division:

o   Control Groups (14 groups): Will use the standard eluent system based on dichloromethane (DCM and DCM/MetOH).

o   Experimental Green Groups (4 out of 18 groups): Will completely replace DCM with a sustainable Cyclohexane / Ethyl Acetate eluent system,

Laboratory Steps:

1.     Preliminary TLC Analysis: Each group will analyze the starting mixture using Thin-Layer Chromatography (TLC) to identify the optimal eluent composition and determine the retention factors (Rf ) of the components.

2.     Column Packing and Elution: Perform silica gel column chromatography, comparing column packing ease and flow rate.

3.     Product Isolation: Recover purified fractions via solvent evaporation

4.     Comparative Data Analysis: Students will compare the results of the 14 standard groups with the 4 green groups in terms of yield, purity, column resolution, and solvent volume consumed.

4. Environmental Impact and Waste Reduction Calculation

·        Direct Elimination of Toxic Waste: Replacing DCM in the 4 green groups will prevent the generation and disposal of several liters of halogenated organic waste.

·        Prevention of Harmful Emissions: Avoiding the incineration of chlorinated solvents eliminates chlorine emissions and reduces the impact on stratospheric ozone depletion.

·        Laboratory Safety Protection: The 4 experimental groups will operate under safer conditions, eliminating exposure to Group 2A carcinogenic vapors and preventing inhalation hazards.

5. EWWR 2026 Outreach and Dissemination Activities

·        EWWR Poster and Seminar: During European Week for Waste Reduction 2026, the Class will present a poster showing comparative data between DCM/MetOH and the Cyclohexane/Ethyl Acetate system, highlighting ecological footprint savings.

·        GCTLC Platform Sharing: The protocol for the optimized experiment will be uploaded to the Green Chemistry Teaching and Learning Community (GCTLC) platform to enable other institutions to adopt the same DCM-free procedure.

·        Future Implementation Plan: Successful results from the 4 groups will serve as a pilot project to fully eliminate DCM across all 18 groups starting in the following academic year.