Aspirin Synthesis ELN Report

Comparative analysis of all aspirin synthesis experiments — yield, conditions, reagents, and user performance

13 Experiments Analyzed 3 Contributing Users Best Yield: 97.61% Scale-up to 1g Demonstrated

Executive Summary

13
Total Experiments
5
Yield-Recorded Runs
97.61%
Best Yield Achieved
25°C
Optimal Temperature
1.0
Optimal Equiv (Ac₂O)
1269 mg
Largest Batch

Key Finding

After early experimental failures yielding only 0.07%, the synthesis was optimized through collaboration between twalker and cnorris. Subsequent runs by twalker consistently delivered 95–98% yields at ambient conditions (25°C, 101 kPa), with DMSO as solvent and 1.0 equiv of acetic anhydride. The protocol was successfully scaled to gram quantities.

Reaction Chemistry

2-Hydroxybenzoic acid + Acetic anhydride → 2-Acetyloxybenzoic acid (Aspirin) + Acetic acid

SMILES (Aspirin): CC(=O)Oc1ccccc1C(=O)O  •  MW: 180.16 g/mol  •  Formula: C₉H₈O₄

Conditions used across all successful experiments: Room temperature (25°C), atmospheric pressure (101 kPa), DMSO solvent, ambient reaction. No heating, reflux, or special atmosphere required. Reaction time recorded as 2.3 h in the largest-scale run (Exp 8455113).

All Experiments — Comparative Overview

Exp ID Experimenter Temp (°C) Pressure (kPa) Solvent Ac₂O (equiv) SA Scale Aspirin Yield (%) Aspirin Amt Purity (%) Status
7616566 twalker — — DMSO — — 0.07% — — Failed
7646818 twalker / cnorris 25 101.0 DMSO 2.0 ~138 mg 91.08% 120 mg 99.0% Complete
7647430 twalker — — DMSO ~1.3 — 0.07% — — Failed
7648111 twalker 25 101.0 — — — Not recorded — — Draft
7648113 twalker 25 101.0 DMSO — — 0.07% — — Failed
7654544 twalker / mbennett 25 101.0 — — — Not recorded — — Draft
7655645 twalker 25 101.0 — — — Not recorded — — Draft
7717625 twalker 25 101.0 — — — No data — — Draft
7736551 twalker — 101.0 — — — Not recorded — — Draft
7748191 twalker 25 101.0 DMSO (10 mL) 1.0 100 mg 97.46% 128.4 mg 99.0% Complete
7803209 twalker 25 101.0 DMSO 1.0 100 mg 97.61% 129.0 mg 98.7% Complete
8455113 twalker 25 101.0 — 0.91 1000 mg 95.34% 1269 mg 98.0% Complete
8455148 twalker 25 101.0 — ~0.9 ~500 mg 97.52% 649 mg 98.0% Complete

SA = salicylic acid (2-hydroxybenzoic acid, limiting reactant); Ac₂O = acetic anhydride. Experiments 7648111–7736551 were created but yield data was never finalized.

Yield Comparison — All Recorded Results

Exp 7616566
0.07%
Exp 7647430
0.07%
Exp 7648113
0.07%
Exp 7646818 ★
91.08%
Breakthrough
Exp 8455113
95.34%
Scale-up
Exp 7748191
97.46%
Exp 8455148
97.52%
Exp 7803209 🏆
97.61%
Best

Note: 5 additional experiments (7648111, 7654544, 7655645, 7717625, 7736551) had no yield data recorded and are excluded from this chart.

Reagents & Conditions Analysis

Parameter Early Failures (0.07%) Breakthrough (91%) Optimized Protocol (95–98%)
Temperature Not recorded / 25°C 25°C 25°C
Pressure Not recorded 101.0 kPa 101.0 kPa
Solvent DMSO DMSO DMSO (confirmed 7748191)
Acetic Anhydride ~1.3 equiv (7647430) 2.0 equiv (excess) 1.0 equiv (stoichiometric)
Salicylic Acid Scale Not recorded ~138 mg (1.0 mmol) 100 mg → 1000 mg (mg to g)
Reaction Time Not recorded Not recorded 2.3 h (Exp 8455113)
Product Purity Not recorded 99.0% 98.0–99.0%
Registered Lot None SPO-06864 SPO-20610, SPO-20611
Stoichiometry insight: Reducing acetic anhydride from 2.0 equiv (used in the early 91% run) to 1.0 equiv (stoichiometric) actually improved yields to 97–98%. This suggests the excess reagent was not beneficial, and stoichiometric conditions are optimal for this synthesis. The large-scale run (Exp 8455113) used a slight deficit (0.91 equiv Ac₂O), still achieving 95.34%, indicating acetic anhydride was the limiting reagent in that run.

User Performance Analysis

RB
twalker
Primary Experimentalist — All 13 Experiments
Experiments created 13
With yield data 7
Early yields (0.07%) 3 failures
Optimized yields 95.34–97.61%
Best single yield 97.61% (Exp 7803209)
Largest batch 1269 mg (Exp 8455113)
Avg yield (completed) 96.99%
CW
cnorris
Collaborator — Key Breakthrough Contribution
Experiments modified 1 (Exp 7646818)
Yield achieved 91.08%
Conditions 25°C, DMSO, 2.0 equiv
Product registered SPO-06864 (purity 99%)
Role Established first high-yield protocol
MT
mbennett
Contributor — Training / Draft Work
Experiments modified 1 (Exp 7654544)
Yield recorded None (draft)
Conditions set 25°C, 101 kPa
Status Experiment not finalized

User Ranking by Yield Performance

1st — twalker: Consistently achieved 95–98% yields after optimization. Best individual yield 97.61%. Successfully scaled from 100 mg to 1 g batches. Demonstrates mastery of the protocol.

2nd — cnorris: Contributed the first successful high-yield run (91.08%), which served as the template for twalker's subsequent improvements.

3rd — mbennett: Involved in one incomplete experiment with no yield data. Cannot be assessed on output quality yet.

Key Findings & Recommendations

1
Early experiments failed catastrophically (0.07% yield). Experiments 7616566, 7647430, and 7648113 all recorded near-zero yield. This was likely due to incomplete procedure execution, missing steps (e.g., insufficient reaction time, incorrect workup), or data entry errors rather than true chemical failure.
2
The breakthrough run (Exp 7646818, 91.08%) established the correct protocol. Edited by cnorris, this experiment used 2.0 equiv acetic anhydride, 25°C, DMSO solvent, and yielded 120 mg of aspirin at 99% purity. This run appears to be the reference protocol for subsequent work.
3
Reducing acetic anhydride to 1.0 equiv improved yield to 97–98%. The optimized runs (7748191, 7803209) used exactly stoichiometric acetic anhydride (1.0 equiv) and achieved 97.46% and 97.61% respectively — outperforming the 2.0 equiv run. This is likely due to cleaner reaction profiles with less side-product formation.
4
The protocol is robust and scales well. Experiment 8455113 demonstrated gram-scale synthesis (1000 mg salicylic acid → 1269 mg aspirin) with 95.34% yield and 98% purity over 2.3 hours. This validates the protocol for production-scale batches.
5
5 experiments remain incomplete with no yield data. Experiments 7648111, 7654544, 7655645, 7717625, and 7736551 were created with conditions logged but products never finalized. These should be reviewed, completed, or archived to maintain ELN data hygiene.
6
twalker is the highest-performing user. Across four completed, fully characterized runs, twalker achieved an average yield of 96.99% (range: 95.34–97.61%), with consistent purity above 98%. This represents excellent synthetic execution of the optimized protocol.

Registered Aspirin Lots

Lot Number Experiment Experimenter Yield (%) Amount Purity (%)
SPO-06864 7646818 cnorris 91.08% 120 mg 99.0%
SPO-20610 7748191 twalker 97.46% 128.4 mg 99.0%
SPO-20611 7803209 twalker 97.61% 129.0 mg 98.7%
Not registered 8455113 twalker 95.34% 1269 mg 98.0%
80332 8455148 twalker 97.52% 649 mg 98.0%